Ok I'm having some idle issues with my s4 t2.
Ok I have a rtek 2.1 with stock everything else. So I do the step by step to set up the idle and it's stays around 725-800 rpms. The after about 10-to 15 minutes it drops down to about 600-675 rpms and sometimes lower and try to die. I checked the timing, checked and changed the tps, checked for a vacuum leak, and I check the bac valve. And it's still doing the same thing. What else could it be??

 

Make sure the two wires in the BAC plug are not pulled back and not mating w/the BAC. If the car were idling low you could push upwards on the wiring just below the plug and see if it changes the rpm/sound of the engine.