95M Passat 2E. Idle problem

[muddy]

Having had 3 previous 2E engined Passats that never gave a moments trouble the latest one is playing up.

When the engine starts from cold, it won't hold a warm-up tickover. It sounds lumpy and dies. If you give it a tiny bit of throttle to try and hold 1,000rpm - then it hunts very regularly between 500rpm and 1250rpm. If you give it a brief rev. and then take your foot off it drops down below tickover and dies.

If you persevere and get it warmed up then you can get it to tickover at around 900rpm but it still seems slightly lumpy. When revved warm, it will drop back way below 900, 'stumble' anf then come back up to 900.

Have cleaned idle stabilisation valve with carb cleaner. No change.
Have swapped idle stabilisation valve for known good one, No change.

Are these typical symptons of a possible vacuum leak or could the throttle potentiometer be dirty or duff ? I have a spare good one to try if that seems a probable cause.
Hope someone can shed some light on this. Thanks.

[lpg boy]

I had similar characteristics with my 2E '95 after a big backfire, resulting in pipes being blown off various fittings on the inlet side. Check all your pipes are tight and there are no splits in them , I have found mine is very sensitive to any form of air ingress bypassing the airflow meter. might be worth seeing if you can borrow an a.f.m. to try, they are also fitted to some audi models.
Don't touch the idle screw or co adj screw as I found it really upsets the ecu when it tries to adjust timing to control the idle speed, causing the timing to hunt wildly(vag-com vag scope illustrates it by displaying a live graph of the timing position.

[Crasher]

Throttle pot failure is common but you should have a fault code read done first.

[muddy]

Thanks for the replies lpg and Crasher.

Crasher. Do the symptoms match up well with throttle pot failure and if I substitute another 'good but s/h' one would it run well enough to prove it was that before I took it to an agent to get the 'new' one matched to the ECU - which I understand is needed?

The spare I have is from a 2E engined Golf that was scrapped because of gearbox problems and engine was running 100% OK.

I will also have a go with a basic code-reader over the weekend.

[Crasher]

Those 2E ECU’s have live data output where it is possible to watch the output of the TPS as a fault code read won’t always show up a fault. The TPS needs to be matched by performing an idling check in basic settings 001 but there is quite a bit more to it than that.

[barryG]

I had this, car would start and drive OK but not idle, just died instantly all the time. Had diagnostic checks and changed a few sensors. A mate found the inside of the throttle body and butterfly valve to be filthy, cleaned it up and shes running fine now.

[Crasher]

Your Passat is a 1995 model with an ADY engine and Siemens Simos injection engine and a motorised throttle body. The 2E engine is a completely different Digifant injection system made by Bosch.

[barryG]

Sorry, Im not a VW expert, apologise for my ignorance.:Blush:

[Crasher]

Sorry to sound arrogant there, the smilie I clicked on didn't appear. It is too easy to seem like a git without a smilie to help. :D

[barryG]

Thats OK, Im not easily offended:biglaugh: