On Sun, 22 May 2011 12:48:46 +0100, "Mrcheerful"
> wrote:

>tony sayer wrote:
>> 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....
>
>have you checked for intake air leaks, particularly the manifold gasket.

That was going to be my suggestion. I had one of these with a no
start condition - a little overenthusiastic use of Holts Cold Start
blew the top of the inlet manifold off. Probably a intake air leak.