Yup, when the idle stabilizer valve begins to fail the engine idle will speed up and slow down as described. It will also permit the engine to die at typically inconvenient times. It isn't hard to replace but it might be costly.

 

HI HAVING VERY SIMILAR PROBLEMS WITH MY AUDI DID YOU GET YOURS SORTED?

 

Something else to consider. I was having problems with the reverse lights and the cooling fan, as well as the instrument cluster. It turns out that on my 1988 Audi 90 these are all on the same circuit with the cooling fan. Like you, I replaced the coolant temp sensor on the radiator, the cooling fan motor, and re-wired the entire trunk to no effect. Talk about tearing one's hair out. The problem ended up being corrosion in the fuse box! It is in a place where water will collect, and things were corroded and shorting out. Cleaning and tightening all the connections cured my problems, after spending hundreds of dollars and countless hours chasing other non-existent problems. It took a savvy old mechanic to figure this one out, and he almost gave up on the car.

 

I have an 88 80 base and struggled with a similar sounding problem for months. It started as powerloss. The more fuel I asked for the less performance I got. I assumed it was fuel related. Then the car started running poorly when cold. I would have to warm it up or it would stall, still had the powerloss but could drive it if I took it easy. Then the real fun started. The car tried to quit on me a couple of times when driving at low rpm's giving me an impending doom feeling anytime I pushed in the clutch, because I was worried I would stall, thus dangerously affecting my driving habits. When I started it later it would run fine if I warmed it up and babied it. (sound familiar at all) Then the car quit altogether. I pushed in the clutch and she just shut off. Out of frustration the car sat for a couple of weeks, until a mechanic buddy told me to test for spark, I coud hear the fuel pump running and I got decent pressure at the injectors using the eyeball test. So we pulled a plug and touched it to the block revealing that I had weak spark. The powerloss,the rough cold running, and the random shutdowns were caused by the distibutor not advancing the spark, causing the engine to try and run backwards when I hit the gas too hard, not burning up a whole lot of gas in the proces. Once we set the timing two degrees advaced with a light borrowed from my buddy. I was good as new. I replaced my tore up knock sensor about a week later to eliminate knock and further advance the timing.

 

Spiffy, im having the issue too, my Dash lights just stopped working and my radiator fan runs like an airplane prop.

I was lucky though, i checked all the fuses before trying to rewire everything, My radiator relay is shot, one of the prongs is straight black lol

I ordered a new one off ebay for 9$.
f*ck you Audi wanting 47$ for it.

 

good job^^,

the idle valve rarely goes bad but does clog up with oil and some time the power to feed it is lost ( I had to rewire mine ) it should have battery voltage when ignition on,
other things to consider with bad idling with these older beautiful babies is the oil dip stick not a jk lol it has an O ring seal on the end so when the dip stick is in it seals it if the seal fails the idle will become erratic

 

forgot to add I bought a new distributor and ignition coil for my car.(for a little under 300$) The timing I set with a light was at the distributor