Misfiring 480

[skipy]

Hi again,
Still the same
Checked temp sensor seems ok (although new one is on the way). wiring sems ok although a little stiff.
Also re-checked distribution system and it also seems ok.
All the spark-plugs are black. which arises one doubt, if it was a cilynder problem only the spark-plug in that cylinder should be black? I mean if (for instance) cylinder #1 did not recieve spark or had faulty injector, would all the sparks be black (ecu trying to compenseate) or just spark #1.
While cleaning the temp sensor (the one under spark-plug #1) i noticed another sensor that is between the distributor and the crank sensor. What is that one for?
Cheers

[doingitsideways]

I think that one is the sender for the guage.
It will have a single spade connector if so.

Black plugs tend to mean rich running, so you must have a sensor out of whack somewhere, either temperature, or maybe Lambda.

Do you not have the code reader on the left hand strut tower??

Steve

Edit:
Just noticed yours is a turbo, may be worth having a read through this on how to set up and adjust your AMM properly.

[1st480]

Hi,
I've had similar issues and found that bad wiring to the Idle Control Valve caused intermitent connection and would find that sometime the idle was normal, sometimes dropped right down to 2/300rpm sometimes high >1200rpm and others surging between ~600 - 1200 depending on how the wiring was sitting.

This also seems to cause an issue of misfires when revving as presumably the engine is seeing various levels of additional air from the ICV when the throttle is in use and it should be at a default position. If yours has a lambda sensor, I'd also assume it does try to compensate for the extra air by richening up causing the black plugs and bad mpg. (Hard acceleration will result in intstant readings of 25.5l/100 ~ 11.1mpg while holding the speed steady with light throttle should show much better instant readings say 13l/100 or less depending on speed and incline, all the way down to 0 l/100 ~99.9mpg when off the throttle slowing down in gear.)

I would check the wiring to the ICV including the connector itself and make that good/replace it. (Also check that the bullet connector mines got a brown wire on the harness to the ICV is not connected to anything else and not shorting out as this moves the ICV to a default low position used only for setting the idle)
Whilst you there you may as well clean the ICV out as they often get plugged up. Note that the bolt holding the mounting rubber bracket needs to be checked as tightened as this can I think if loose allow an air leak.

Then clean/replace the plugs and reset the ECU by disconnecting the battery. Check there are no leaks to any of the engines breathing pipework including small vacuum pipes and the ICV pipework and also check the connectors on the throttle switch and AFM are good and secure.
While under the bonnet check that there is a distinct click when moving the throttle by hand and that it clicks when let go. (If there's no click it needs the swich loosening off (2 cross head screws underneath) and turning till it does (anticlockwise I believe). If turning it as far as possible in both directions doesn't make a click, it will need replacing.)

I'd also, if you have a digital multimeter, check the AFM Ohm reading at this point between the outer 2 pins reads something sensible (between 385 and 600) if not or just to get it set close set it to ~420 Ohm by turning the screw on the AFM while checking the meter.

Now Reconnect the battery and then give the car a good run out.

If this has improved/fixed the issues then it's time to set the throttle and throttle switch, AFM and idle speed correctly to baseline spec.
I'd also clean out the crankcase ventilation unit on the front of the block to the bottom right hand side standing in front facing the car which can also get gummed up.

[skipy]

Hi again;
Thank you both for your help.
the past week the car's behaviour was improved in terms of idle stability.
this weekend I've checked the AFM/AMM. Between pins 2 and 6 it was 589, i've regulated it to 380. I'm not very sure how it works but decreasing the resistance would give place to leaner mixture or the other way around?
It's seems to missfire a little at cold start for the 1st seconds as the engine sounds like an harley. It does not take longer than 5s to become stable. Perhaps I will rise the resistance to 420 and see what happens.
While at it i've checked throttle position sensor. seems OK.
Also went to clean spark plugs (haven't cleaned them the week before to have better testing elements). They seemed alot cleaner which makes me think that this week the engine at least runned better.
Will keep you posted of further developments

[1st480]

Hi,
This is for the TURBO and sorry but it's a bit long at least 2 cuppas worth.
*Apologies for spelling, grammar and any other mistakes, having lost this 3 times due to site/connection falling over at the point of hitting post and power cuts, I’ve rattled it off quickly and have probably missed a few bits.*

Yes, AFM Lower resistance = less fuel/leaner mixture.
Further info and useful pictures on a lot of the below and other jobs on the 480 can be found at www.volvo-480-europe.org where there are many friendly and knowledgeable people.

1st things are for the usual Disclaimer and TLDR: please see the bottom of the article.

Please be aware this is all from memory, I'm not looking at my engine at the minute so a couple of bits may be slightly different such as vacuum ports and location/colours of certain wires etc. I may have missed a tool or gotten the wrong size. Also, I don’t have the HBOL in front of me so I haven’t included all the sensor values and pins to check, only the ones I can remember. Again the forum above is probably a good place to find these if you haven’t the HBOL.
I’d suggest that before anyone follows this guide, they read through it completely first.
Also, for those who have already done some troubleshooting, it has been split into job areas so you can see if there are any bits suggested you haven’t tackled yet.
If you're still having some issues, other areas to check are below:
(Best to give yourself an afternoon for this if possible 3-4 hours the first time you do it and include a cuppa or 3 as this is a fairly comprehensive list of things to go through to eliminate misfires, rough running and bad idle.)
You'll need:

Tools:
Spanners including 6/8/10/11/13/14/15/17
Screwdrivers including stubby + and - and a medium and long handled -
Carb Cleaner & Lint Free Rag
Spark plug socket and ratchet with extension bar
Pliers
Feeler Gauges
Multimeter
Length of wire ~30cm (longer is fine) both ends bare
Fine sandpaper
Fuel proof Gloves
Fuel proof container & tub (tub to bath items in and containers to hold dirty fuel/carb cleaner to be disposed of properly)
Selection of Jubilee Clips small and large to replace any you find broken
Some hose to replace any vacuum pipes you find split (Most is I think 6 or 8mm ID fuel hose will do in a pinch a couple of meters of each would be good to get.)
Selection of Spade Connectors/Ring Connectors(big and small)/New Wire/ to tackle any you find broken
Electrical Connector Cleaner
Possibly a Socket Set
Possibly a small rubber mallet
Possibly small amount of petrol in suitable container e.g. petrol can ( ~1 litre to be used for cleaning)
Possibly a couple of small bolts to block vacuum pipes for blanks
A bit of thick grease
HBOL (The manual will give you some torque figures and possibly some helpful pictures)
Some cable ties to tidy up cable routing if that’s your thing  and clamp vacuum pipes round blanking bolts.
Piece of bright paper. (Plain white is good doesn't need to be very big.)
Nice to have a torque wrench too.
Also nice is something with internet connection so you can search for additional info and pictures e.g. on this site or www.volvo-480-europe.org or the usual favourite search engines.
(Couple of cups of favourite brew and biscuit to help break up the job )

Parts:
I’d suggest getting these before you start in any case as they won’t cost a lot and will help keep your engine in top shape.
Spark Plugs
Air Filter
One way check valve (diesel fuel line one should do or windscreen washer jet non return valve)
Optionally a New Distributor Cap, Rotor Arm and set of HT Leads.
Optionally but a good idea, a New Battery Earth Strap with ring connector at both ends 2-3ft or ~1m should do. (Will be used to add extra battery to engine earth)

1st thing disconnect battery! (Safety and once you have done the following it will mean the ECU has had time to reset.)
For everything below, when I say clean, if you have bought new, you can replace the old parts instead.

Distributor cap:
Take the 3 screws out (1 either side at the top and one slightly awkward at bottom centre) and check all internal pins are clean and corrosion free and no cracks. Also check for oil leaking into the cap. Clean if necessary. (Oil is likely camshaft seal.)
While it is off also clean the rotor arm tip and centre (i.e. the metal part). (Or replace with new if you bought one.)
Also check by removing and replacing one (to keep the order correct) at a time the HT leads for corrosion and that the pins on the distributor cap are secure and corrosion free (Some have removable nipples the same as spark plugs which can become loose.
Tighten carefully as needed just more than finger tight and without putting an angle to your tightening.) [If replacing the HT Leads and Distributor Cap with new, ensure you match the order of the old leads on the old cap with the new leads on the new cap. Also, do check the nipples are tight on the new cap before fitting the leads.]
Ensure HT leads re-seat securely with a click.
Also check the centre - to coil lead, I have found this corroded at the distributor end and the distributor pin likewise! (The coil end was like new!)
When refitting, check that the earth strap is present (should be to the RHS top screw) and making good clean contact at both ends. Don't over tighten the distributor cap as it will crack the lugs.

Coil:
Next, check the coil, there should be 2 small wires bolted to the top; check these are secure and cleanly connected. Also check the HT lead is good at this side (It relies on outside contact to a metal sleeve where it fits the coil, I usually slide the rubber shroud back from the HT end before refitting to ensure it pushes fully into the coil port and then slide the shroud back down.)

While it is out of the coil, check you can see the metal sleeve inside the coil port, and that it is clean and secure.

Ignition Amplifier:
Near the coil on the bulkhead, you should find a small flat black box on a metal plate with a multi connector. Remove the connector and check the pins for corrosion. (Use your connector cleaning spray then re-seat the connector.)

Finally near/under the coil, there will be a single wire (grey and black I think) coming out of the loom most likely spade connector-ed (New word?) to another which goes to the amplifier.(I think, it should be obvious when looking which I mean.) This I've seen corrode badly; check it by separating the spade connector, being careful not to strain the other ends of the wire and clean/remake/replace connector as necessary. I have previously put a joining wire in as the connectors were corrosion welded together and fell apart on separation.

Spark Plugs:
Check each spark plug is not sooted up badly and check/adjust electrode gaps if you can. (Clean/replace as necessary) [If replacing with new still check the electrode gap and tightness of nipples.]
Check that the nipples are secure on the top. (Just beyond finger tight should do. You can put them upside down in a spark plug socket and use pliers to nip them up the last bit carefully)
A fiddly bit is check and clean the spark plug hole seats in the engine. Careful not to drop any muck into the engine! If you can, plug the hole with lint free rag. (This is where the bit of thick grease on the end of long handled screwdriver can also help as you scrape the crud carefully and the grease picks it up/sticks it to the screwdriver rather than it falling into the engine. Clean any grease off after with the lint free rag.)
If there's lots of muck they won't seat/seal right...carbon build up may be a sign that previous plugs have not been tight enough.
Refit the spark plugs and tighten correctly.
Check the spark plug end of each HT lead before fitting and ensure it clicks into place correctly.

Throttle:
Remove the pipe to the throttle body and check/clean any oil/carbon/muck with lint free cloth + carb cleaner. Also move the throttle to fully open to clean behind the butterfly and where it sits in the throttle body.
Use stubby flat head screwdriver and remove the bypass screw (brass to the front of engine side of throttle body with it fitted, it may have a anti tamper cap over it)
Check the rubber seal is good on this screw and that the screw is clean.
Clean the bypass hole with some carb cleaner and also squirt some the other way (the air path comes from lhs in front of the throttle butterfly you should see a ramp like part)
Refit the bypass screw and tighten gently till it bottoms out.
Loosen the throttle stop nut (6/8mm nut) and back the stop bolt off (Thin flat head stubby screwdriver) till it is no longer touching the throttle arm and check that the throttle cable has a little slack here so it's not holding the throttle open.
(A piece of bright paper underneath the throttle arm can help for the next bit.)
Screw the stop in till it just touches the throttle arm, then tighten 1/4 turn.
Hold the stop in position and tighten the stop nut to prevent movement.
Check the throttle cable has a small amount of slack still.
Check the Throttle Position Switch (TPS) underneath the throttle body (Small cross head stubby screwdriver)
Remove the multi connector and check for corrosion to the pins and wear to the wires, clean/repair as needed)
Check that the smallest movement of the throttle makes a click from the TPS, if it doesn't, loosen the 2 screws underneath and twist the TPS fully in both directions and you should hear a click. If no click is heard, the TPS is probably in need of replacement.
Once you're happy it has a click, turn it anticlockwise slowly till it clicks.
At this point hold it in place and carefully tighten the LHS screw on the TPS (This is the easiest one to get to) Recheck the click is made from smallest movement of throttle and also check a couple of times opening the throttle fully and letting go so the spring pulls it back shut to ensure the click always occurs. Adjust again if necessary and once happy tighten both screws.
Now reconnect the multi connector.
Next, with stubby flat head screwdriver back the bypass screw out 5 turns.
(It seems strange that it's so many turns for anyone used to setting up a carb, but don't worry this should get the engine running to start with and hopefully fairly close to an accurate setting.)

Cold Start Temperature Sensor:
This is located near the #1 spark plug (Transmission end) on the front of the engine block and has a 2 pin multi connector.
Remove the multi connector and check for corrosion to the pins and for damage/wear to the wiring. (I found it was fairly tight/short wiring from the loom)
Clean/replace/repair as needed and refit connector.


Idle Control Valve (ICV):
Remove the multi connector (3 pin) and check for corrosion to pins and wear/damage to the wiring...Again, they seemed to make it a little bit short, I've had to replace the connector and extend the wires previously.

If you have time, remove the ICV by removing the 2 (13mm I think) bolts holding the rubber mount and then the 2 air pipe off the end of the ICV.
Look inside the end, it should be clean metal and you should be able to turn the valve door inside with your finger. Clean using carb cleaner and lint free rag. For further cleaning, block one side and fill with carb cleaner or petrol, block 2nd hole and shake vigorously, then empty into sensible fuel safe container. Refill, block and leave to stand upside down/or soak internals using petrol in fuel proof container. (In a well-ventilated area away from flame sources, etc. Use sense, stay safe and environmentally friendly) Dispose of dirty cleaning fluid safely.

While the ICV is off, check knock sensor, (Black circular sensor with bolt through centre, just below where the ICV mounts) remove connector and check pins and wiring for corrosion/wear and sort as necessary.
Loosen bolt and remove sensor, check block is clean behind the sensor.
Refit, carefully!! They don't like to be too loose or tight. Loosely mount with the bolt through the centre, then position sensor so the connector port is to the left around 9o'clock position. (This is so it isn't blocked by the ICV and its mount when you refit it. Check by offering the ICV rubber mount up to the block once happy with position put ICV mount to one side and continue) Finger tighten the bolt then torque correctly if you have the torque wrench, and the manual/net will tell you how much...If you haven't a torque wrench, after finger tightening, use a spanner and tighten approx. 1-2mm i.e. just tight enough that you can't undo by finger!

Grab a cuppa if you haven't already!

Empty the ICV if not already done and check it's clean and free moving internally. Allow any vapours to evaporate.
While that's drying, it's probably the best time to remove the crankcase breather.

Crankcase Ventilation Breather:
The Crankcase Ventilation unit is on the front of the block to the bottom right hand side (standing in front facing the car) looks like a cylinder in a foam jacket with a clamshell like valve on top, which can also get gummed up like the ICV.
The breather is push fit into the engine block, and the valve on top has 2 pipes going to it.
Getting it off may need the small rubber mallet and the large 17+mm spanner as a wedge under it. There's not a huge amount of room but with the ICV still out there should be a bit more room on that side. Work it side to side and use the spanner if needed underneath till it comes free just take your time.
Separate the valve off the top carefully these can be really brittle!
(I think you need to remove the foam jacket first.)
You'll probably find the breather is thick with carbon and old oil gunge.
Again you want the petrol/carb cleaner bath see above, I’ve left them soaking overnight before for really clogged ones but a quick clean now should help.
Once you've given it a couple of vigorous shakes with some cleaner in it, stand it on one end in the tub and fill with cleaner/petrol then leave to soak.
You need to check the valve operation at this point as they often break causing crankcase pressure to build under boost. (Not good and leads to oil leaks and potentially leaks onto clutch giving a ruined slipping clutch) Also, it can cause bad running throughout the rev range.
The port that connected to the inlet manifold should only blow through in the direction of the inlet, if you can blow the other way, clean it out (you may find an orange part in there that used to be the built in check valve) and fit the check valve in the tools/items list into the pipe from the inlet ensuring it's the right way round to only let air got to the inlet! (You may need to replace the pipe with one a little longer.)
Leave the Crankcase ventilation unit soaking and continue with putting the ICV back on.

Refitting the ICV:
Refit the ICV, put it into rubber mount first then connect the air pipes. Now bolt the mount into place, bottom bolt is a bit fiddly due to space. Ensure that the mount bolts are tight as I believe the top one if loose will introduce an air leak.
Reconnect multi connector. Check you haven't lifted the oil dipstick up as the harness goes near here and can catch it.
Check that the single wire, mine has a brown one, with bullet like connector off the ICV wiring harness is not connected to anything and not shorting out...this is used to set the ICV to a default position for setting the idle only and should not be connected to anything at any other time. In some cases there is a 2nd wire to earth nearby with the opposite connector, if these are connected together, disconnect them as they shouldn't be except for when setting the idle.

Air Filter:
Remove and check the air filter is clean, replace with new one if needed.
But don't fit it yet.
While the air filter is off; Check the next items:

MAF:
Remove the multi connector and check for corrosion at pins and damage to wires. Clean/repair as needed.
Check that there's no oil or obvious grime on the mesh either end. And if you look through you should just be able to see a thin wire (goes through 3 angles passing through 3 hoops if I remember right looks a bit like a light-bulb filament)
While it's off, use the multimeter set to ohms and check between the outer 2 pins. Set to 420 ohms by turning the screw clockwise to increase value and anticlockwise to lower it.

Don't refit yet.

Crank Sensor:
Look down to the top of the gearbox where it connects to the engine, you should just be able to see a small cylinder with a wire coming out of it poking up from a curved flat bracket. This has 2 x 11mm bolts holding it in place, undo these and lift the sensor up and out. Disconnect the wire which will lead to a connector a short distance away toward the front of the engine.
The sensor is magnetic, and picks up crud on the end. Check this is clean with lint free rag and also with it out, check the gap it fits into on the gearbox/engine is free of grease and muck. Check the wiring and connector are corrosion and damage free and then refit and reconnect it.

Turbo Piping/Diverter Valve: (Optional to check these beyond pipe to pipe seals)
Towards the bulkhead, starting from the pipe you removed the MAF from you'll find all the turbo pipes, including about half way down the engine bay height, to the transmission side of the engine bay, sat in the middle of a thick pipe is the diverter/blow off valve with a vacuum pipe coming out and leading off toward the throttle body.
Check all pipes are connected securely and show no signs of splits/cracking.
Any that are broken will need sealing/replacing...wrapping in electrical tape should do for a temp repair but replacement is the way to go.
If you want to upgrade/check your diverter valve, now is the time to do it. A popular upgrade is the VW/Audi 710N valve instructions can be found on www.volvo-480-europe.org/forum.
It is held in by a jubilee clip top and bottom. It should open when there is boost pressure from the turbo AND a vacuum in the manifold (I.e. when you go from hard acceleration boost to off the throttle e.g. for a gear change) OR, if the boost pressure is above its spring rate. It should seal under other conditions. If this isn't the case it needs replacing or possibly cleaning if the seal has gunged up.
Once you're happy the pipes there are air tight and good condition including the vacuum pipes to and from the turbo itself, be very careful checking these vacuum pipes as there are 3 that terminate at a small black box bolted to the bulkhead (Boost solenoid valve) [AFAIR 1 goes to the wastegate actuator, 1 goes to turbo housing and one goes to the intake] which has very small, usually brittle ports that snap easily, you can move on.

Airbox Earth Lead (+Lambda connector if fitted):
Just before we start putting things back together, there is a flat braided earth strap running under the airbox, (Mine goes from the wing to the aircon drier unit, yours may be different or maybe the actual earth terminal to battery) you will probably need to use the pliers to stretch the rubber bungs to lift the box off its mounts and to get it back on after. (It makes sense when you see it.)
Unbolt the earth strap from both ends and check it's in good condition and the mating faces and mount points are clean the refit. If this is damaged, it will need to be replaced.
You should also find the connector plug for the Lambda sensor down near the air box separate and check for corrosion/damage and reconnect. (You can trace it up from the sensor itself on the exhaust if you can't spot it easily.)
You can now refit the airbox base, stretching the bungs to pull them though the mount holes on the base.

Refit the MAF to the pipework and then the air filter(New if needed) and top of filter box checking that all the pipes you took off are back on and secure.

Cuppa time again...On the home straight now!

Empty the crankcase breather if not already done and check that it doesn’t look gunged up inside. (You may be able to see some perforated baffles I think)
Ensure that the top and bottom port are clean and free of gunge on the outside also and leave the breather to stand empty to allow any vapours to evaporate.

Earth Points:
Next there are a few earth points/bundles to check and clean. Each front wing has a group of earth wires bolted to it...towards the front I think there are ~3 on RHS and ~4 on LHS (when stood in front of the car facing towards the car.)
Next there are 2 bolted to the engine lift eye on LHS top of engine (when stood in front of the car facing towards the car.)
I think there may also be a couple near the alternator.
There may be a few more that I've forgotten, but I've mentioned the ones I remember being important.

Other Electrical points:
Check the connectors on the back of the alternator are clean, corrosion free and secure. Bad connections here can cause power to fluctuate and cause running issues. I’ve also seen the posts for one of the ring connectors on the back of the alternator be loose from the alternator but with the ring connector tight to the post. Removing the ring connector then carefully tightening the post with a 10mm spanner before refitting the ring connector fixes that.

Vacuum Ports:
The engine has a few vacuum ports that should be blanked or connected to a pipe. A leak will cause issues throughout the rev range including idle.

Please be aware I'm not looking at my engine at the minute so a couple of your ports may be the connected the same or some may be connected on some on some of them that I have/remember blanks. The important bit here is mostly no leaks. Blanks shouldn't leak and pipes should be secure and leak free.
On the LHS of the inlet manifold, there are 3 ports, 1 is to a hard pipe which disappears off to the wing and AFAIR is the port to the boost gauge and tee’d off to the ECU in the centre console for its on-board MAP sensor.
The other 2 should be blanked.
The throttle body has 1 port blanked off and another closer to the engine that is to the diverter valve/possibly tee’d.
There is also a larger port to the back of the inlet manifold on the RHS that should be blanked.
You should also check the ECU vacuum/boost pipe at the ECU side and the tee to the boost gauge.
The quick/dirty way; Remove the engine side and suck, quickly block port with tongue... if it sticks and holds vacuum it should be ok.
Better way is to check both ends and ensure pipes are secure and hold both vacuum(with opposite end sealed off temporarily) and can be blown through...i.e. are not blocked with both ends open.
Get to it by putting the Driver's seat (On a RHD) front seat fully back and remove the carpet piece on the side of the transmission tunnel. The ECU is there low down and toward the handbrake. The pipe connects to the left of the main ECU connector; you should be able to follow it down from toward the front of the transmission tunnel where you'll also find the tee to the gauge. Blowing through from this end should be easy and prove no blockage. Trace up to the gauge as well to ensure no leaks.
Make sure pipes and cables are secure and refit carpet.

Refit Crankcase Breather:
Time to refit the breather, check that the hole in the engine block is clean for a good seal, don’t let any bits all in as they will land straight in the oil so block the hole with a rag before cleaning around it. The breather should just push firmly into the engine block, a couple of light taps with the rubber mallet may help if you’re struggling.
Then fit the valve back on top of the breather, and reconnect the pipes to the correct ports, the thinner port connects to the pipe going to the intake manifold (Which should now have a one way check valve in it. Check that the pipe isn’t kinked flat! If it is you will need to use some new hose to lengthen it till you have it connected with a gentle kink-free curve.) And the other one disappears under the throttle body and towards to turbo piping near the bulkhead.

Battery:
Just before we reconnect the battery, check all the wires connected to the battery terminals...there's probably 4-5 on each post usually with ring connectors.
Check the cables are held firmly in the ring connectors and that the wires and connectors are corrosion free. The wires can often be a bit loose in the connectors or the connections a bit corroded. Clean/fix as necessary. Do this for both terminals.
Also, now if you have it, is the time to add that extra earth strap to the –ve terminal and bolt it to the engine block. There should be a bolt on the alternator bracket on the front of the engine block you can use as the mount point if you have a cable that will reach. Alternatively, there are other places that can be used such as the bolts to the lifting eye closest to the battery.
Then, ensuring that the terminal itself and the battery posts are clean and not broken, reconnect the battery +ve first then -ve. You shouldn't see any big sparks.

Setting the Idle! :
Now, the car needs to be warmed up.

Start the car, hopefully your idle should be close and fairly smooth don't worry if it is a bit slow or fast (if it's really horrible check you haven't left a pipe of connector off. Obvious culprits being the ICV/TPS/MAF/Cold Start Temp Sensor connectors/HT leads and the vacuum pipes on the inlet manifold)
Let it idle for a few minutes till water temp shows 40 deg C then rev it gently 3-4 times to ~2000rpm and come off the throttle to check it doesn't die.

Next, take it for a drive. You need to warm it up fully till the fans have kicked in at least twice. (Be gentle, revs under 3000 and turbo gauge in the white as much as possible till oil is up to 70 deg C then drive a bit harder. )

Once up to temp and driven for probably 15-20mins, stop, turn the engine off and here is where you need the length of wire. Near the ICV is that earthing connector mentioned. You need to put one end of the wire into the connector and the other end not earthed just yet.

Get your stubby flat blade used previously for the bypass screw.
Start the car, the take the free end of the wire and earth it. You should find that the revs change usually lowering. Now leave this earthed and check the revs on the dash.
We want them to be ~700rpm.
Turn the bypass screw clockwise to lower the idle and anti-clockwise to speed it up. Quarter turns are good, keep checking the rev counter till you have it set nicely at ~700rpm.

Next, disconnect your ICV earthing wire and the revs should jump back up to 800-900rpm. Check the oil dipstick hasn't lifted out of its tube.
On pushing and releasing the throttle, you should find the revs rise nice and quickly with crisp response to the throttle then fall quickly to about 1200rpm then slowdown more gently to an 800-900rpm smooth idle.

If you really want you can now reset the ECU again by disconnecting battery earth terminal for 30 minutes or so. Now is a good time to go in grab something to eat and drink. Then, reconnect your battery and take the car for a mixed driving route how you'd normally drive for it to relearn your driving style and enjoy a smooth stable idle with much better response from the engine throughout its rev range and more MPG.
There are other things it could be, these are the things I’d start with and run through first.

TLDR:
Spark plugs/HT Leads/Coil & Ignition Amplifier and connectors/Distributor cap & rotor arm/Air filter/ICV + wiring/Crankcase breather should be clear & check valve should only work 1 way allowing air into the inlet manifold not from manifold to breather/Throttle setting (stop screw touching arm + 1/4 turn)/TPS (click on opening throttle) + wiring/Throttle Bypass Screw (~4-6turns out)/MAF ~420ohm between outer pins/Vacuum leaks/Earth Points/Crank sensor + wiring/Lambda sensor + wiring/Air intake pipes leaks/Other wiring including battery terminals and alternator.

Disclaimer:The information in this article is intended as guidance only and is provided "as is" without warranty of any kind whatsoever. The author shall not be held responsible or liable, under any circumstances, for any damages to your vehicle, yourself or anything else, resulting from the use or inability to use the information within. Use sense, take care and be safe

[skipy]

Hi again,
The car has been behaving ok. Thanks you very much for your help.
The only thing i'm founding strange is that before i've regulated the maf the spark plugs were practically clean. Ever since i've regulated the maf, the engine runs a rough for the first 5~10 secs when cold. After warming up i can feel a faint petrol smell (at the trunk and not at the driver side). so today I had a look at one of the sparks and it was black on one side which means the mixture is till rich. What's strange is that as I said before the sparks were clean before I regulated the maf. but if it was regulated from a "richer " position how come that happened.
Once again thanks for your help guys. The car is much healthier now.
Best regards;
skipy
BTW 1st480 thanks for your very complete maintenace procedure post

[mhuk]

Volvo 480 Europe club is good for old posts on problems.

[skipy]

Hi guys.
The car is still not 100%. But is a lot better.
I'm currently searching for a throttle position sensor (posted in wanted section) as i've had some troubles with it in the past. If anyone knows of a good one please let me know.
Thanks for your help

[skipy]

Hi guys,
So...about 2 weeks ago was talking with a guy that lives near me which has a 480 with an B18ftm engine (same as mine ). He told me that in the past he had a similar issue (floating revs) and the issue was with the turbo's recirc valve.
So one day when the engine was starting to behave bad, I went and puled the vacuum line from the recirc valve. imediatelly, the engine settled.
I thought to myself that maybe the recirc was to blame. I had a 710N valve in the garage so I replaced it. No Luck, after 4 days the car was the same.
I puled the vacuum hose and again it settled.
So, it seems i'm close now. It has to do with that vacuum line (the one that comes from the trottle body). I had already done the sugestion of 1st480 (once again thanks) but must have done it wrong.
This weekend I'll try and do the check again.
BTW: the vacum line that comes from the throttle body goes to the recirc valve and that valve that is connected to the icv (can't remember the name XD) but it also splits and goes to other location anyone knows where it goes to? i loose it when it goes near the radiator.
Lets see if this is it.
Steve, Sorry if i'm carrying your post trough wrong paths.