I've got an A6 Audi Avant, in fact a bit of a vintage one 1995!, olde lady has done 198,000 plus miles and 'tho shes olde she still moves around very gracefully and still is fleet of foot when required.. In fact shes more used as a "works van" these days and a very comfortable one too:) However one minor fault plagues her in that she won't tickover (idle) all the time. In this model which is a straight 2 litre petrol it has the ABK engine code Digifant system which uses an idle control valve which sets the idle via a voltage that opens or closes that valve rather quickly.
Symptoms are, Starts fine 'tho seems to be as if shes over choked and after a few minutes running the idle speed hunts from around 800 to 1500 RPM as if you were blipping the throttle.
A quick flick of the ignition switch to off and back on again makes her idle at 820 RPM which is the correct rate. However once your off again shes back up to her hunting tricks.
And again quickly switch the ignition off and back on again sets it to idle fine.
Now some times it will almost behave in that she will idle but just on the 1000 RPM mark and sometimes albeit rarely she will behave properly and idle at 820 RPM. Same as before if shes at 1000 a quick off and on has her pick up the 820 RPM setting.
I have changed the idle valve as that was playing up before which was causing frequent stalling and now if you disconnect the idle valve it will rev away around 1500, connecting it back up again sees it coming right at 820 when you just have the engine on tickover and stationary.
The small garage where I normally take it they have a visiting Auto electrician who put it on his analyser who said it seemed alright and no fault codes that he could see of. Our local main dealer said they didn't have that diagnostic unit around anymore either. So before I start changing bits on a trial basis anyone ever had this before and any idea which part of the system it might be causing that?.
Perhaps I should take the garages advice and get a younger model but while this ones running fine apart from the above and has passed the last 10 odd MOT tests with sod all wanting doing I'd like to hang onto her for a while yet:)...
TIA....