Engine 850: B5254S/2.4/20v: Volvo 850 - low or missing idle

[hammerpaal]

Hi!
First time on this forum.

I have a Volvo 850 which has recently been serviced by me.
Overall driving distance is 308' KM.

Parts that has been replaced/repaired:

Fuel pump - genuine Volvo
Fuel pump relay - genuine Volvo
Throttle body gasket - Victor Reinz
Vacuum tree with o-ring - genuine Volvo
Air intake hose - genuine Volvo
PCV-system with flame trap - genuine Volvo
Cleaned Idle Air Valve Control
Intake manifold gasket - genuine Volvo
Cleaned throttle body thoroughly
Replaced injector seals, filters, etc.


My problem is related to idling, both cold and warm engine. It seems like the signal for fuel mixture is missing so it does not compensate whether it it is cold or warm.
I have located some vacuum leaks and fixed them, but it ain't good enough.
The vacuum tree has nearly every ports connected to something, but two of them are not in use.
I have blocked these with vacuum caps, but the car isn't running properly.
When I remove one of the caps, the car runs at 1000 RPM when warm.
Have been using some starter fluid to check for leaks, but there is no change in RPM, so that should indicate that there is no leaks.
The only DTC I have from time to time is "2-2-3 IAC valve opening signal", but the IAVC is humming when the engine is not running, which indicates it is receiving power.


When the car is running, it is running great and there is no hesitation, no back firing, no smoke that indicates wear and tear - absolutely no problems when driving it.

What should be checked further?

Vacuum check valve?
Brake booster vacuum hose - does this affect idle if it is leaky?

[capt jack]

Have you taken the IACV off and cleaned it through? It may well be sticking a little. Just because it's receiving power doesn't mean to say that it's actually opening and closing as it should.

It's quite a simple mechanism, and from memory I think it's very easy to remove and to clean.

Cheers

Jack

[hammerpaal]

Originally Posted by capt jack

Have you taken the IACV off and cleaned it through? It may well be sticking a little. Just because it's receiving power doesn't mean to say that it's actually opening and closing as it should.

It's quite a simple mechanism, and from memory I think it's very easy to remove and to clean.

Cheers

Jack

Hi, Jack!

Yeah, I have cleaned it with WD-40 and used a rag to remove build ups. Also used compressed air can to blow all the way through. Three wires are connected to the IAVC. If one of them are the power cable, what are the others? Signal cables?
The motor is of an early design, so it is not like the later ones. I can recall I have read something about the change of design, because of sticking valves.

In another forum one mentioned that the ECU could be faulty and not sending pulsing signal to the motor.

Have already tested two motor and no effect.

Spoke to a local garage and they could point me to cleaning the throttle body and the butterfly (which I have already done), and replace the camshaft sensor. I don't know if this sensor has something to do with idling, but I have no codes on it.

[capt jack]

Hi there.

The fact that the car is running well except at idle, and that the only DTC is IACV-related would suggest that the valve is the problem - either this has a problem itself, or there's an electrical issue with one of the cables - one of the signal ones that you've identified would be the best guess.

Sounds like you've already looked at all the obvious problem areas, but you don't mention any of the ignition components.

If it's an 850 20v I guess it has a conventional distributor and rotor? I think I'd start by checking all the spark plugs - make sure that they are correctly gapped and of the right spec. Then have a good look at the leads. If possible run the engine with the covers off in the dark, so you'll see if there's any arcing or sparking. Then take the distributor cap off and examine it for signs of wear or cracks, and look at the rotor. Clean everything up and make sure that it's all put back together properly. Replacing the rotor and cap isn't too expensive, and new spark plugs shouldn't break the bank. Even new leads are not too expensive. I got my V70 to 300,000 miles (480,000km) but found that the rotor, cap and leads needed to be cleaned every 50,000 miles (80,000km) and replaced every 100,000 miles (160,000km).

Other than that I guess other more obscure problems could come from a poor connection of the engine earth strap, or an air filter not properly fitted, or maybe the 'cold start' valve in the airbox that diverts warm air from over the exhaust could be faulty.

Then again, you might have a failing MAP sensor.

But I think the place to start is with the ignition.

Cheers

Jack

PS: I believe that if the camshaft sensor fails then the engine probably won't run at all, and at the very least you'd get a DTC.

[hammerpaal]

Originally Posted by capt jack

Hi there.

The fact that the car is running well except at idle, and that the only DTC is IACV-related would suggest that the valve is the problem - either this has a problem itself, or there's an electrical issue with one of the cables - one of the signal ones that you've identified would be the best guess.

Sounds like you've already looked at all the obvious problem areas, but you don't mention any of the ignition components.

If it's an 850 20v I guess it has a conventional distributor and rotor? I think I'd start by checking all the spark plugs - make sure that they are correctly gapped and of the right spec. Then have a good look at the leads. If possible run the engine with the covers off in the dark, so you'll see if there's any arcing or sparking. Then take the distributor cap off and examine it for signs of wear or cracks, and look at the rotor. Clean everything up and make sure that it's all put back together properly. Replacing the rotor and cap isn't too expensive, and new spark plugs shouldn't break the bank. Even new leads are not too expensive. I got my V70 to 300,000 miles (480,000km) but found that the rotor, cap and leads needed to be cleaned every 50,000 miles (80,000km) and replaced every 100,000 miles (160,000km).

Other than that I guess other more obscure problems could come from a poor connection of the engine earth strap, or an air filter not properly fitted, or maybe the 'cold start' valve in the airbox that diverts warm air from over the exhaust could be faulty.

Then again, you might have a failing MAP sensor.

But I think the place to start is with the ignition.

Cheers

Jack

PS: I believe that if the camshaft sensor fails then the engine probably won't run at all, and at the very least you'd get a DTC.

Yeah, I would get a DTC if the camshaft sensor was bad.
After a lot of brain activity the last few days I have concluded three possibilities, either defect IAVC, faulty signal to the IAVC or faulty ECU.

The IAVC may not be as clean as it should and it could also be sticking so the valve won't lift from closed position.
The signal cable for opening is broken somewhere between the ECU and the IAVC, or the contacts are corroded and needs to be cleaned out so the pulsing signal can easily be transported to the IAVC.
The last option is that portion of the ECU that controls the IAVC is toast.

I'm now pretty sure there is no vacuum leaks, and the system is air tight.
When it's idling at 500 RPM and I remove one of the vacuum caps, the idle goes to about 1000 RPM. As I see it, the air that is sucked into the vacuum tree compensates for the closed off valve in the IAVC. - But still, the idle is a little bit fast.
Also, because of the missing open signal to the IAVC, - then the cold and warm air/fuel mixture will also be missing at start-up.
I now think the problem is getting solved at last, I will do some more testing in a few days and I will come back if I find something more of interest.

Captain Jack, thanks for the contribution so far.

[kdan]

just a question................

what should these idle at????

[capt jack]

Originally Posted by kdan

just a question................

what should these idle at????

'Bout 800 to 850, but it should be steady, certainly more than 500 and not as much as 1000.

If taking off a vacuum tree cap speeds it up then that suggests that left to it's own devices, there is not enough air getting in during idling. Which does indeed point to an IACV not being as open as it should be, or a throttle body that is very dirty.

The old B20 and B30 series engines in the EFI engines fitted to the 164, 1800E and ES and the 140 series had a similar arrangement (yes even 40-odd years ago!). The IACV was opened and closed according to the coolant temperature. A clever idea but horribly unreliable. The valve was given to seizing up in warm weather - when it was not needed, so that on cold days it was well and truly stuck.

In effect the IACV acts a bit like a choke would on a carburettor car, but instead of the driver manually adjusting it, as the engine warms up so the valve should adjust automatically. So imagine trying to get a carb'd car to idle cold with the choke pushed in, or warm with it pulled out. You'd be all over the show. And if the IACV is getting giving duff information about it's status to the ECU it will in return get bad instruction from the ECU, and so round and round will the problem go.

Happy days!

Jack

[t+m]

when i had a small air leak on one of the vac pipes it caused the idle to raise,but you can chech for vacuum with a cheapo vacuum gauge,most cars show 20-21" of depression if there are no significant leaks but i would guess the idle valve is the culprit, check out the part num and cross ref it to see what else it fits because its a bosch system it will be common to other cars,then see if you can source one from flea bay.It must have either returned a signal to the ecu that was outside of its parameters or not sent a signal at all which is what set up the fault code so its got to be prime suspect.