Idle problem - what else to try???

[jameswkr]

Engine gurus - pls help. Car starts and runs fine from cold. Idles @ 1000 rpm and drives ok. If in traffic from cold, revs drop slowly down to c 800. At the first and subsequent stops ( until really hot ) revs drop to near stall and then jump to 1200 or so before stabilising at 800 or so. Once hot it will tick over fine with very little overcorrection. Putting lights on has no affect on idle speed. Disconnecting the ISV raises revs but leaves the car jerky and unrefined at low speeds - so I assume the ISV (all clean and lubed) is working...if the radiator fan comes on whilst idling, the revs jump to 1200 and re stabilise ( unlike putting the lights on )....
Checked and rechecked so far ( and to spec ) - throttle pot, coolant temp sensor and wiring, intake temp sensor, MAF outputs/inputs, all hose connections, vacuum and boost seem OK. Car has new plugs, lambda probe is within spec ( MOT passed easily ).

Anybody have any other ideas ? Can the ISV be lazy on certain inputs ?
...Just starting to get very irritated that this problem wont be solved..it spoils an otherwise nice car....and is driving me crazy !! Thanks James.

[Al@work]

Hi James
I would have presummed the symptoms would be the ISV but after reading your thread its possible but not a definate i would therefore go to one of the local meets get the car on vag com and maybe swap with a member the isv and then see if it cures your problems
That way if it sorts it then you know your cure if not at least you can eliminate it

Hope this helps

Al

[rotoryboy]

get the car on vag com

Yep, We VAG com'd one at weekend and it had failed totally

[giventxodreams]

I would try lowering the idle speed. I had the same problem on my car and I dropped the idle speed to 900 or so and it quit doing it.

[jameswkr]

Thanks for your input ( @Travis, this is Bosch Motronic on ABY S2 - no idle adjustments possible - fast idle isnt the issue - its bouncing idle on decelleration ). Is it possible for the ISV to have the correct resistance ( 7 - 11 ohm, mine reads 8.9 ) but still not work correctly? Any kind Forum members able to help with VAG COM please - willing to travel/reimburse...

[A80Avant]

old thread but same problem,...
assume jameswkr has used the VAG COM and reveiled no fault codes...

then what?

could it be any of the following?
1)potentiometer?
2)air leak of the hoses going to the ISV?
3)throttle body itself?

Is the way of controlling the idle speed as described on MJS technic or calibrating it,used in these engines?

[A80Avant]

well,what i tried today was change back to my old paper air filter and guess what?Everything came back to normal!Of course big difference in the 1000-3200 area building up a lot slower,but at least i have a BIG BIG difference when the turbo kicks in,which brings a smile to my face!

On the other hand,idle is as smooth as a baby! How come gurus???why would an air filter cause all this trouble?Is it the mtm chip not being calibrised to accept the better flow?Is my MAF trying to tell me something??....who knows?

[Billman]

Engine gurus - pls help. Car starts and runs fine from cold. Idles @ 1000 rpm and drives ok. If in traffic from cold, revs drop slowly down to c 800. At the first and subsequent stops ( until really hot ) revs drop to near stall and then jump to 1200 or so before stabilising at 800 or so. Once hot it will tick over fine with very little overcorrection. Putting lights on has no affect on idle speed. Disconnecting the ISV raises revs but leaves the car jerky and unrefined at low speeds - so I assume the ISV (all clean and lubed) is working...if the radiator fan comes on whilst idling, the revs jump to 1200 and re stabilise ( unlike putting the lights on )....
Checked and rechecked so far ( and to spec ) - throttle pot, coolant temp sensor and wiring, intake temp sensor, MAF outputs/inputs, all hose connections, vacuum and boost seem OK. Car has new plugs, lambda probe is within spec ( MOT passed easily ).

Anybody have any other ideas ? Can the ISV be lazy on certain inputs ?
...Just starting to get very irritated that this problem wont be solved..it spoils an otherwise nice car....and is driving me crazy !! Thanks James.

Your problem is that when the fan comes in whilst idling and th eRevs rising ?