Erratic / rough idle in 8P S3 - and how it was fixed
Just thought I'd post this for the sake of anyone that gets these faults and decides to use the search function:
I had rough idling - When pulling up to a stop, the revs wouldn't drop all the way down to ~800rpm, instead lingering around 1000rpm and then slowly rising to approx 1300rpm and then finally dropping back down to ~800rpm where it should be.
Eventually the CEL came on and the following codes were logged:
001287 - Idle Control System RPM: Higher than Expected.
P0507 - 001 - Upper Limit Exceeded - Intermittent
008583 - Bank 1; System too Lean at Idle
P2187 - 004 - No Signal/Communication - MIL ON
The internets told me I should be suspecting a vacuum leak and Audi investigated it:
First they blamed the PCV, claiming it was stuck open... The valve was replaced (with 06F 129 101 L) and the gasket too (with 06F 103 483 E). Problem came back on the drive home.
Next they spent quite a while inspecting all the hoses and said they found a very slightly leaking seal... Got the car back and the problem came back down the road. Had the head tech stumped and the car was booked in again.
Finally they discovered a fuel pressure sensor was faulty. It was replaced (with 06E 906 051 K) and the car has been fine since.
Interestingly enough, after the PCV was replaced, the faults never actually reappeared on their VAS system, but were showing on VCDS. The tech put it down to VAS not logging certain faults until they have occured a certain number of times...
Hope this helps someone in the future.