AudiWorld Forums - FIXED: Engine stumbles and hunts all the time

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FIXED: Engine stumbles and hunts all the time

Posting this as advice for others having a similar issue to the one I had.

A year ago, my 2006 started "hunting" when I'd drive it slowly up a hill. Meaning, it was like an intake leak - the engine would oscillate at a higher RPM then lower every half second or so. No codes (never any codes!!!) - Audi test looked at it, said its fine (obviously no codes so its fine, right?!?!?!).

Over the next year it got worse and worse. Then when cold, driving up the driveway, it would start bucking. It got a better when warm - sometimes the issue would go away. But over time, even at freeway speeds, the engine was "hunting" - it just never settled in to one RPM.

VCDS showed no codes. I did a throttle adaption 10 times - no change. I started a VCDS Thread that you can read if you really want to see all the things I did to resolve the problem (over a month!).

In the end, I was directed to clean the throttle. It was SLIGHTLY dirty - tiny bit of carbon on it, but heh, why not. While it was out I decided to check the gears and see if there was any obvious issue. When I took the black cover off, I saw the potentiometers. Now, I knew they were in the car, and I had looked at their values in VCDS - but GEE WHIZ - this is 1920s technology in a 2006 $50K automobile from Germany! Grrrr.

Anyway, I decided to CAREFULLY clean the tracking pads with a Q-tip and 72% alcohol. I got a small amount of visible black material - I assume it was particles from the pad that had flaked off due to wiper.

Put the thing back together CAREFULLY and re-installed the throttle. Used VCDS to first do a throttle adaption, then reset the engine codes (see VCDS thread for why this is important!).

Started the car drove it around the block - no hunting or stumbling. Its now been well over a week, and the car is operating perfectly!

Since I didn't do each step separately, you decide what cured the problem:
1) cleaning a tiny minuscule bit of carbon from around the throttle plate
2) cleaning the potentiometer contact pads

I seriously hope my experience resolving my issue helps someone!

PS: the throttle plate:
https://cimg1.ibsrv.net/gimg/www.aud...798b8ee5d0.jpg

Well done!!! Most of the time, we don't have to look too far, the culprit is something simple right under our nose.

Thanks for the thread - this might help me and for sure will help others. My car will oscillate with rpm going up and down when driven at constant throttle and I've seen plenty of threads on this. Even some folks being convinced by Audi garages to pay for a new torque converter.

I already bought a replacement TB but haven't fitted it yet as the problem isn't so bad during warm weather, it's in the cold air that it plays up. I think I'll follow your advice and first take off the old TB and clean it up along with the potentiometer tracks also. Then if that fixes the problem I can sell the new TB.

What did you clean the TB plate with ? You mentioned alcohol for the potentiometer tracks. I have isopropanol here.

is it just those 4 screws visible in the photo which secure the TB (after removing the intake hose)?

What are and where are these potentiometer contact pads? Thanks.

I believe that once you remove the throttle body, there is an access panel on the side (black plastic panel) which can be unscrewed to access the motor, gears and electronics, including the potentiometers. However I haven't done this yet, so hopefully the OP will shed some light also.

Dhoerl,
Can you please tell me where the potentiometer contact pads are? Thanks

This guy explain it really good... pay attention...there is a black cover on the side of TB held by few clips... remove clips and gently lift up the cover...

...

This next video is better explanation about those contacts, but TB is Volvos...but you will get the point.

Quote:

Originally Posted by Sverige (Post 25187564)

What did you clean the TB plate with ? You mentioned alcohol for the potentiometer tracks. I have isopropanol here.

isoprop should be just fine! or something like CRC contact cleaner =)
cheers!/H

Quote:

Originally Posted by Nurke (Post 25189433)

This guy explain it really good... pay attention...there is a black cover on the side of TB held by few clips... remove clips and gently lift up the cover...

https://www.youtube.com/watch?v=fdLA5pXUkk4 ...

This next video is better explanation about those contacts, but TB is Volvos...but you will get the point.

https://www.youtube.com/watch?v=6-2Ui1PXQPc

I just got a chance to watch both of these. Very good info. I saw The potentiometers and how the teeth on the gears can get worn down. Good stuff. Thanks.

I hadn't subscribed to this thread so missed the posts til now. I used carburetor spray cleaner. I seriously doubt the tiny bit of carbon on it caused my problem.

Also, yes, just 4 screws. The TB threads into a plastic holder- its so odd - not what you'd think. Then there is o-ring that provides the seal. Thinking about it - maybe the TB wasn't properly mated to the o-ring - that would have caused the issue too I suppose.