Audi Repair: idle drop, switching gears, vacuum system

Question
QUESTION: I have a 96 A4 quattro.  Ever since I bought the car (about 3 years), the idle will drop for a second then come back up to normal.  It will do this ever couple minutes or so sitting at red lights or anytime the car is idling.  Every so often it will stall, but usually the idle will come back up just before  that happens.  Could you give me some ideas as to where I should start looking.  Thanks

ANSWER:  hi there,

Sounds like your having a problem with the idle control circuit, whats the current mileage of the vehicle?? are all the filters ok?? especially the Air and fuel filter? what about the plugs?? are there any other problems associated to the current fault?? lack of power, hard start??

sometimes the throttle valve gets clogged with carbon and cant function properly, try removing it and cleaning it. it should be relatively simple. just don't touch any adjustments. it would be a good idea to mark the positions of anything you remove so that you can put it back in the same position when your re-installing.

Also check the intake for any leaks, inspect the vacuum system for disconnected or broken lines.







---------- FOLLOW-UP ----------

QUESTION: Hi again, thanks for the quick response.  It has about 140,000 miles.  I had major service done about 6 months ago, timing belt, hoses, plugs, filters, etc.  I was hoping that would fix the problem but no luck.  I've never had any problem with starting and power seems fine to me.  Sometimes there is a little lag under hard acceleration when switching gears, but I just assumed it was the 140,000 miles on the original clutch, which is probably the next thing on my list to replace!  Thanks again.

Answer
Again, I'd start with the throttle valve, with time carbon builds and this can cause restrictions in the idle valves, and make the throttle stick. the clutch would cause lack of power especially in hill climbs and difficulty changing gears. some times it causes the idling to increase but i doubt it would cause the stalling and eratic idling.

before changing the clutch check the biting point. put the car in geaqr and slowly release the clutch with out pressing the accelarator. note the point that it 'bites'. it should be at at the bottom near the floor, if its higher up that would indicate the clutch friction material is worn out.

also it would be helpful if you could have a diagnostic report so I can advise you further.