Audi 80 2.0E - Revs won't come down!

[AudiMT]

When stationary, if I rev the engine to say 3k to 4k rpm, the revs stay high. In fact, above 4k rpm, they can start to increase! It's the same problem when driving except, when applying the brakes, the revs will eventually drop but it takes a while. The car is idling about 1200 rpm and the idling isn't erratic.

If I disconnect the electrical connector to the idle control valve, the revs drop to a more normal 800 to 900 rpm. Put the connector back on and they jump to around 1200 rpm. I tried cleaning the ICV and I think it's made the situation worse. I also tried another ICV from an old Golf GTI - exact same part number. It didn't really make a difference except this time when I removed the electrical connector to the ICV, the engine stalled.

I looked for vacuum leaks as there is a vacuum pipe that goes into the main inlet manifold. If I pump the brake peddle a few times, the revs will rise a little - not sure if that's normal.

It's an anti-stall feature! 🙂 It's annoying as the car is always screaming and not great when trying to change gears. Is this an ICV problem or is there something else going on?

Thanks!

[Steve Q]

Could it be the MAF sensor?.

[AudiMT]

Thanks for the reply, Steve. Apologies for the extremely late reply!

I managed to get to the bottom of this. It turned out to be the coolant temperature sensor - blue one, 2-pin (025 906 041A) - the one that goes to the ECU. There is another one next to it - white-one, 3-pin (053 919 501A) - which goes to the gauge in the instrument panel.

Basically, the blue sensor was telling the ECU the engine was still cold and so added more fuel, raised the revs in order to try to heat it up, if my understanding is correct.

The old one was reading around 250k ohms at around 12 degrees C  and the new one was reading around 3.5k ohms at the same temperature, according to my notes!

After the new sensor went in, the revs dropped and have stayed fine ever since. I'm not sure what the idle revs are supposed to be but there are few other issues with the car, so the revs might be a tad too high. They are currently around 900 rpm.

[cliffcoggin]

Thanks for that detailed information Mohammed. It will defintely be useful for others.