Engine 850: B5202S/2.0/10v: Idling problem

[petrolblue]

I've got a 1996 850 saloon 2.0 10V manual (B5202FS) with 94k miles. I've had an idling problem that's been ongoing since I bought the car about 2 and a half years ago but it seems to be getting worse recently. When pulling the clutch in as though to change gear or when coming to a stop the revs will sometimes sit at about 1500 rpm. It tends to do this intermittently, perhaps about half the time. Normally a quick blip of the throttle will settle the idle speed but on rare occasions it just won't settle down at all. The main reason for me wanting to cure the problem is that I can feel the car pushing me when I am OFF the throttle when the revs drop to around 1500rpm in gear, for example if I'm slowing down to stop or in slow moving traffic the car will start pushing me forward. Also it feels very snatchy on/off throttle.

I've trawled this forum and google and checked everything I can think of. I've taken off and cleaned the IACV, cleaned all the electrical connections, taken out and cleaned the MAP sensor, checked vacuum hoses visually and they all look pretty new, cleaned and lubricated the throttle body, adjusted the throttle cable and lubricated the mechanism and thrown a can of Wynns intake cleaner down it. Since my ownership it has also had new rotor arm, plugs and HT leads. If I unplug the IACV the revs raise significantly to about 2-2.5k rpm so it seems it is working at least to some extent? There are no warning lights on the dash.

Is there anything else I should have a closer look at or that I haven't checked? Could it be something to do with the automatic choke, coolant temp sensor or throttle position sensor perhaps?

Many thanks for any help

Scott

[Baffler]

If you have a multi-meter you can check for resistance of the ECT sensor. At 20°C it should be ~ 2800 Ω and at 90°C ~ 206 Ω.

It does sound as though there are still deposits in the IACV. When you were cleaning the valve did you happen to rotate the spindle, fully to the left and right, to check for carbon/tar deposits and scoring? You can use something soft like a wooden skewer to maneuver the spindle and cotton ear buds to remove any deposits.

When cleaning the throttle butterfly valve did you clean both sides?

[petrolblue]

Hi, thanks for your reply. When I cleaned the IACV I did move it fully left and right. I sprayed brake cleaner in until in ran clear but I didn't physically get anything inside to clean it, so you think it could be IACV related still?

I do have a multimeter but I'm not massively clued up with electrics, how would I test the ECT, is it just holding the meter terminals across 2 pins on the connector?

Regards

[Baffler]

Originally Posted by petrolblue

Hi, thanks for your reply. When I cleaned the IACV I did move it fully left and right. I sprayed brake cleaner in until in ran clear but I didn't physically get anything inside to clean it, so you think it could be IACV related still?

It's not recommended to place anything inside the chamber, for fear of irreversible damage, but if you can see any traces of tar/carbon or feel any roughness in the spindle travel it will need further cleaning. There could very well be a hardened piece of carbon lodged where you can't access it.

Holding the valve with one hand (nitrile gloves a must) block one hole with your finger, fill the chamber with cleaner, block the second hole and using a clockwise/anticlockwise motion of the wrist you will feel the spindle travel back and forth.

I tend not to lubricate the IACV or TB as it can attract dust and grit but, if you must, try using a dry lubricant such as a PTFE spray.

Originally Posted by petrolblue

I do have a multimeter but I'm not massively clued up with electrics, how would I test the ECT, is it just holding the meter terminals across 2 pins on the connector?

Yes...set your dial to Ohms (Ω) to check for resistance across the two pins.

[960kg]

When some owners take their motor in for service instead of the mechanic cleaning the IACV some just alter the throttle plate adjustment to bring back a decent idle.

Then when the owner has a problem with idle and cleans the IACV the idle will be high due to the previous mechanic altering the throttle plate screw ,so just turn it back down until the throttle plate is almost damn nigh shut as there are air bypass holes in the throttle housing.

[petrolblue]

Some great advice thank you, will keep you posted how I get on.

[AndyT5]

Have you checked the throttle cable for sticking / affecting throttle butterfly position Vs accelerator pedal?
If idling at 1500 rpm and you restart the car, do the revs go back to 1500, or back to normal ( not touching accelerator).
I currently have a different idle problem to you I think!

[petrolblue]

Interesting thought but I haven't tried that. I will do next time it does it! I have lubricated the entire throttle mechanism but I have not checked that the actual throttle body is completely shut, it could be that it is not quite shutting and the idle control valve is struggling to compensate for it. It's just so hard to drive smoothly when it jerks on/off throttle.

Well I've bitten the bulletin and ordered a new IACV and TPS from parts for volvos as they weren't too expensive and at least I know they're good, as chances are they'll both be past their best anyway. I've decided to take the throttle body off completely and clean it and while it's off to do the 960 throttle plate mod or to shave down the plastic restrictor, so while it's off I'll swap the TPS. I've also got 5 Volvo OEM sparks, an air filter and throttle body gasket from PFV pretty cheap and will do a mini service at the same time (oil was changed November). May wait til weather warms up slightly to do it

[petrolblue]

Originally Posted by AndyT5

If idling at 1500 rpm and you restart the car, do the revs go back to 1500, or back to normal ( not touching accelerator).

I currently have a different idle problem to you I think!

I've tested this a couple of times now and when I restart it always goes back to 1500 rpm.

What idle problem have you got Andy?

[Rick Barton]

I see you changed the rotor arm but I didn't see mention of changing the distributor cap. I have changed them in the past to very good effect on the running of the engine.