928 S4 idle surging only on hot start
 

I have been having an issue with my 88 S4 where the idle surges only on hot starts and will sometimes die out if I do not hold the throttle. When the engine is cold it fires right up and idles perfectly. The MAF was replaced a couple of years back and I replaced one of the fuel pressure regulators as it was leaking. Any ideas what else it may be?

Its possible that the ICV is clogged up and may just need a good cleaning. They can cause a similar condition when they're gummed up

Your car should have a single fuel pressure regulator and 2 (different styles) fuel pressure dampers.

How long ago did you replace the one FPR/FPD (which one)? Have you checked all of them since you have started having the idle issues?

Could be a sticky IAC as mentioned by Matt.

I would also suggest checking for vacuum leaks. If you have access to a smoke machine, I have had great luck using them to find leaks. don't forget to check the entire system including the charcoal canister in the right front fender.

have you verified the correct functionality of the idle switch on the TPS?

Revisiting this. The car has been in the shop for 3 months now, trying to find the issue.

Replaced the idle valve, replaced mass airflow meter, rebuilt intake, checked idle switch, new temp sensor, checked O2, fuel check valve, good vacuum still nothing. After it dies out the first time on hot start the second start fires right up.

Could a DME rebuild potentially solve this?