1.8T AGU idle revs issue

[lowforce]

Hi guys, I'm new to the audi-sport.net forums community although I have been rolling my A3 8L for a couple of years.
Lately the car ('98 A3 8L 1.8T stock) has some serious idle revs issue which drive me crazy since I cannot find a solution.
The idle revs are unstable, drop down to 500 only at lower speeds, especially when I put to neutral at 50 km/h and below. Until the full stop the revs keep dropping up and down (500-1100), after that they are pretty much stable and OK (around 820-840). At higher speeds there is no such thing. Did some tests yesterday, accelerated up to 100 km/h and above and put to neutral. Then the revs are OK until speed is around 50 km/h.
The throttle body has been replaced with a VDO OEM one last year, no issues with adaptations or any fault codes. Several months ago replaced the DV with the 710N, seems to be working OK. Did several checks for boost leaks, did not find any. The MAF was tested, got 120 g/s and there were not any faults according to VAG COM.
Any help or advice would be appreciated.
Cheers.

 

[lowforce]

Hi, did some more tests today and observed the following:
Idle rpm are becoming more unstable as the coolant temp rises. No issues with coolant temps below 60-70 degrees (as per the dash indicator)
Accelerated up to 120 km/h and put into neutral - at 120-80 km/h idle is almost OK, at 80-50 km/h are becoming unstable (around 700-900 rpm) and at 50-0 km/h the rpm become erratic (400-1000), the headlights flicker. :O
I also scanned with VAG COM and have the following fault:

16500 - Engine Coolant Temp. Sensor (G62): Implausible Signal
P0116 - 35-10 - - - Intermittent

Plan to order this temp sensor and replace it, however I'm not sure if this will fix the issue
Any further ideas?

 

[adz_a3]

sounds like an air leak issue. best thing is to get it smoke/pressure tested. also remove intake air temperature sensor near the throttle body and give it a clean. just be careful not to break the wire though. been known to cause a rough idle.

 

[lowforce]

adz_a3, thanks for the advice.
The problem is finally solved. Although the TB was replaced recently and looked not so clogged I gave it a clean. I didn't remove it, only used dry cloth. Started the engine, drove a little bit and the idle was pretty much OK, was never so stable before.