I have a 97 SS A4 and have an issue where after the car is up to temp and been driving a little bit if I stop at a stop light the engine will develop a rough idle.
I has never died on me, just gets a vibration I can feel through the car and doesn't run smoothly. If I ease of the brakes and let the car roll it is fine. If I put it in park it will idle fine and smooth. Only seems to do this when warm and on the brakes.
Moving it's fine, plenty of power.

I just did new opti, plugs, wires, and EGR valve. Had a new fuel pump put in 3 months ago. I'm thinking it might be the IAC valve acting up. Just curious what you all might recommend to look at.

 

Leaking brake booster? Had that before...

 

Maybe slow iac response also

 

Also could do a smoke test to confirm if there is a air leak