A6 Audi "Hunting"!...

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....
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Tony Sayer


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tony sayer wrote:

have you checked for intake air leaks, particularly the manifold gasket.
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On Sun, 22 May 2011 12:48:46 +0100, "Mrcheerful"

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.
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If it has a throttle body ? I'd try cleaning it and getting it re-aligned. Also a vac leak sounds likely
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tony sayer laid this down on his screen :

vacuum leak or sticky idle valve.
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I'm not sure about that ECU, but some will rev up the engine if it appears that a cylinder has stopped firing while idling. Check the spark plugs after idling the car to see if one looks extra grimy.
It could also be a broken wire on that valve. Audis aren't known for excellent wiring. I just fixed two wires on my 07 A3 that had been crimped into connectors so tightly that they broke off. I see lots of wires into engine block components that are missing a strain relief.
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The normal answer is Vag-Com, but given you're presumably local to me we could plug it in & see what it thinks it's doing whilst it's hunting.
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Yes I believe I may well be, but anyway I'll have a look at the weekend for leaks first then perhaps I'll drop you a mail
Thanks to all for your suggestions..
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1996 A6 1984cc ABK petrol. The Idle control v v can be taken apart and cleaned with WC40 or the like. The thing with the electrical connector comes out of the plastic air intake and the rubber hoses. You'll see the v v part and you can push it in or connect it to the battery and see it work. Spray into the v v to clean it. The thing with the electrical connector on doesn't come to pieces without hacking it. Find the engine control relay, on my A6 it is in the passenger footwell at ones left foot. This can cause lots of problems. It has a number. The computer is also down in there to the front where it can get wet if the drain above gets blocked. Pull the big long connector off and put it back on again, have a look for white powder or discolouration on the contacts. Spray it with WD 40. There is info on the net, pos in this forum. Check all the inlet hoses and connections. Check all the wiring connectors, pull them off and push them back on again. An Autodata CD has some info. The Throttle sensor is at the bottom of the throttle housing. There is a setting for the Throttle you'll see an adjusting bolt just at the end of the throttle wire on top of the throttle housing. If this is worn or loose then it could cause the butterfly flap inside to close. Dirt can accumulate on the butterfly v v and inside the inlet manifold. I'll not go into detail here as there is a lot that can be done to sort this little problem, however there was a lot of info on the web about this type of problem. It'll be easier if you have a book / CD. The Auto data and another that I got didn't have everything in them about the A6. The Haynes isn't a lot of good these days but it might be better than nothing, I have never had a Bently workshop manual so I can't comment on it. A nice big multimeter is good, one with large numbers is better as sometimes one is some distance from it when doing checks. You can get a thing from Gendan that reads fault codes. A garage may not have the information to do a check on the idle control v v. Some of the checks are done with the engine running and if I remember there is 14v and 5 v.
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It has already been changed and yes, it does work the engine note alters when you plug and unplug it.
Odd but when its hunting up and down the rev range unplugging that does cause it to settle when plugged back in?...

Yes changed..

All clean and dry..

Well thats clean..
I'll check the operation of the throttle stop and sensor.
FWIW changed the water temp sender, well both of them as the motor factors had them going cheap, anyway its now slightly better when really warm tends to behave a bit more i.e. correct idle speed for longer.
And the water temp gauge works;)..
thanks for all who helped .. appreciated...

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1996 A6 1984cc ABK petrol.
It has already been changed and yes, it does work the engine note alters

Some of that era had a get you home setting on the computer. So when the ICv v is unplugged the computer may go to, get thee home mode. One possible way to check that is to uplug the ICv v and then drive the car and see if the speed is limited.
Odd but when its hunting up and down the rev range unplugging that does

Could be because the v v is closed and it takes a little time for the comp to adjust to the new info'. The MAF shall show a slight vacum/low pressure/ volume/flow of air = less fuel needed. If there is a small leak on the inlet system after the MAF/VAF (and other names) the leak can cause the exhaust oxygen content to be higher and so the O2 sensor on the exhaust informs the comp so. The comp adds more fuel and so the see saw hunting occurs. If the O2 sensor is malfunctioning it can cause hunting. If the fuel rake pressure is too high/low it'll cause hunting. If there is wear on the HAL sender spindle the timing can fluctuate as it can do it the timming belt is worn or the tensioner a bit stiff. Loads of other stuff, too much to type about.
FWIW changed the water temp sender, well both of them as the motor

And the water temp gauge works
The CT senders have to be same as the originals, ie their resistance needs to be within a window if they are not then the reading of the senders can be wrong. The VIN number needs to be used to get the correct ones.
e.g I put a gauge sender from an A4 onto the A6 and it showed 52C. I put another sender on and it showed 92C.
Basic settings needs to be done somehow, I have not found out much about it except that I need to pay for it to be done, it's not been done for 5/6yrs.
Our local main dealer said they didn't

There is info' on the web about VAGCOM which is (maybe) the diagnostic gear. There is an american company that sells (www.ross-tech.com) software which can be put into a laptop (size counts) and there is a cable (special bit) to connect up to inside the black box with some of the fuses and relays in. On mine this black box (there are several black boxes) is on the RHS (UK) under the lid in the plenum below the drivers wiper.
Auto

The fault codes are in the comp' not in the ICv v. The diagnostic connections/connectors are not the same for OBD1, 2,3. The lecky ud need the connectors for that vehicle type and yr(s). He'd also need a VAGCOM or the Ross Tech type thingy to get accurate readings and the workshop manual to do the tests as one needs to know the voltages/ resistances. The voltage/resistance can be done with a multimeter but one needs to make up wiring to carry out the checks. Still a lecky who is familiar with the make and yr could know where to stick the probes etc and what to expect.
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Well thanks for all that Donk, interesting stuff.
Well the temp gauge registers fine (90 deg C) and on one or two days last week she was almost behaving tickover at 820 RPM all the time, other days up to the olde tricks. Seems a bit temperature related it seems on the day when all was almost well it was around 12.5 deg outside so its a good pointer as any. Might take her out later when its colder as deffo the other day when it was hot she was at it again.
Still overall its a bit better so going in the right direction:)
cheers all...
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Tony Sayer


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