Very odd T5R problem

[Niles]

Not my car but a mates. T5R manual M reg. When the cars running it idles at 800rpm very smoothly. Rev it & the revs build to 6500 no problem, however, the revs take ages to drop. Sometimes it behaves, I went out in it tonight & gave it some welly, go's really well but when at 'giving it some' the revs don't fall between gear changes & when coming to a halt allowing the engine to help with slowdown (trailing throttle) the revs still stick up around 4500-5000, then sits for a second or 2 then slowly falls.
Really annoying bit is that if you pull over & rev it while the cars standing still the revs seem to behave.
Throttle body has been cleaned & linkage isn't an issue. Can't see any air leaks & as the idle is perfect an air leak isn't really a suspect.
Turbo blows nicely.
Any ideas? The owner is getting majorly tired of it.

[Taff - t5]

Have you cleaned the air idle control valve?
The revs tend to stick when its full of c--p!!

[Jod T5]

IAC valve comes to mind http://www.volvoforumsrepairs.org.uk/800Repairs/iac.htm , also the operation of the recirc valve spring....
Cheers
jod

[Niles]

Have you cleaned the air idle control valve?
The revs tend to stick when its full of c--p!!

not sure mate if its been cleaned. at idle the cars fine. May well be worth a good look & clean!!!

[Niles]

IAC valve comes to mind http://www.volvoforumsrepairs.org.uk/800Repairs/iac.htm , also the operation of the recirc valve spring....
Cheers
jod

why the spring,do you think that a tired spring won't release the pressure & hold the pressure in the cylinders?

[Niles]

just been told the Idle Control Valve is spotless & squeeky clean.

Any further ideas other than the recirc valve spring? (it will be investigated)

[Saaamon]

Same problem on my 850R its very annoing, would like to find a solution.

[Dangerous Dave]

Have you checked the throttle flap (sounds noobish I know) it gets the crud from the PCV system on it, obviously this would also mean that the IAC valve should be fouled up too, but its not always the case. Its another thing to scratch off the list.

[PaulZX]

I get the same thing on my T5.... I'll be watching this thread with intrest...

[Dangerous Dave]

Also, to check the IAC valve, disconnect the multiplug, there should be three pins on the IAC. Connect a multimeter (set to resistance) to pins 1 and 2, then pins 2 and 3. The reading should be 9 to 14 ohms.

You can also check the movement of the valve by removing the assembly and twisting the body back and forth, you should be able to hear the valve moving inside. If not, then it might be stuck/sticking.

HTH

Bomb

[marky 76]

i had the same problem on my c70 and i ruled out airleaks ,,,, BUT i found the problem was indeed a airleak on the inlet manifold gasket ... sounds very much like it,s getting more air from somewhere !!!!!!!!!!!!!!

[Niles]

Have you checked the throttle flap (sounds noobish I know) it gets the crud from the PCV system on it, obviously this would also mean that the IAC valve should be fouled up too, but its not always the case. Its another thing to scratch off the list.

The throttle body & flap have been cleaned. My mate who owns the car is a very VERY experienced mechanic & the problem has lost him already & doing his head in.

So, things to check are..... Recirc valve & inlet manifold gasket. Boost control solenoid???

[Dangerous Dave]

Fair enough mate, hope he gets it sorted, seems like its affecting quite a few people.

[Tomcat]

Sure it's not the throttle cable?, sounds like it from the syptoms. If you have a spare then why not swap it just to be sure?.

[flyingbrick]

Ye mine has the same problem this winter. Cant remember it doing it last summer. It seems to have gone away at the moment. touch wood.....

[Saaamon]

The throttle body & flap have been cleaned. My mate who owns the car is a very VERY experienced mechanic & the problem has lost him already & doing his head in.

So, things to check are..... Recirc valve & inlet manifold gasket. Boost control solenoid???

Had anymore luck yet mate?

[roryscott30]

I posted a message a few back and unlike you got almost no response, thanks guys. I struggled on and carried out the same checks as you. I researched the problem to the temperature sensor and got a new one from Rufe and it has cleared up. Mine was along the same lines erratic revs which can be a classic case of TS fault. New one is around £20 and in any case worth a try.
Other things to try are lambda sensor which should really throw up a code.

It's nice to get replies when you're tearing your hair out!

[callyuk]

This is a common issue on the 850's my T5 does it as well and was told by a few people that the only real way to elimiate it was through a remap although cleaning out throttle body ect. does help

[850twr]

i had this problem untill i fitted my forge dv and blanking plate, so the original recirc must of been at fault. made a big difference .

[Alan M]

I disconnected and blanked off the pipework to and from the PTC in the Maf pipe and cured this problem. Even with new pipework and clips from Rufe mine still had a rise in revs with the throttle closed until it was cured by venting the PCV to atmosphere and blanking off the nipple on the side of the inlet manifold.

[Saaamon]

This is quite clearly a common problem on 850's, it would be good to come up there a checklist of possible faults that may cause this to happen, as it seems there are an array of different causes.

[BruceT]

I too suffer this problem.

Most notably when changing from 1st gear at 1800-2500rpm to 2nd gear. When depressing the clutch the revs will increase 200-300rpm and then slowly drop which makes the gear change clunkly unless you adapt the way the change gear (Ie, bring the clutch up slower)

I posted this on the VOC sometime back and was told this is common on all T5's due to the large/weigthy flywheel and the excess air in the intake tubing having no where to go.

Im venting my PCV system to the air and have a custom maf to turbo pipe which is fully sealed.

A dump valve and a blanking plate for the turbo sorts this problem as far as im aware 99.9% of the time as the excess air is vented out and thus revs drop like a normal car.

Maybe it is the aged stock CBV not working properly or maybe its the excess air in the intake which causes the problem.

Additionally, when coming off the throttle my car still seems to be accelerating slowly which would be the same as above (Increase in revs due to air having no way to go so i assume its going through the iac into the engine and accelerating slightly)

Things ive done

Removed and cleaned IAC
Remove and cleaned throttle body and plate
Stage 0
Removed pcv from intake system

[callyuk]

Dump valve never solved the problem on mine i just learnt to cope with it

[Jod T5]

I disconnected and blanked off the pipework to and from the PTC in the Maf pipe and cured this problem. Even with new pipework and clips from Rufe mine still had a rise in revs with the throttle closed until it was cured by venting the PCV to atmosphere and blanking off the nipple on the side of the inlet manifold.

Interesting theory Alan, by blanking off the inlet manifold i would expect you would be running extra lean, especially at WOT...At boost pressures my understanding is that the nipple allows inlet manifold pressure to bleed to the post metered inlet, pre turbo....By blocking this off the inlet pressure is higher, giving more boost but this is not matched by the Map....
Cheers
jod