I have a 2002 Audi S4 (2.7 V6 twin turbo with automatic transmission). I was going around 50 - 60 mph when all of a sudden my speed started to drop (the gas was on empty, don't know if that has to do anything with this). I pulled over, turned the car off, restarted it and the EPC light came on (car won't go more than 10 mph). Now when the engine is running the rpms go up and down a little and the car shakes. Also i hear sounds (like exploding) once in a while (i think through the exhaust). I got those two codes: P0638 - Throttle Actuator Range/Performance (Bank 1) and P2101 - TAC Motor CKT Range/Perf. Did anybody had this problem before? I'm thinking maybe it sucked water or bad fuel at bottom of fuel tank since it was almost empty. Please help!

 

P0638 throttle actuator control, bank 1 - range performance problem faults are basic setting not carried out ( if applicable ) ISC actuator/throttle motor, APP sensor.

I guess the other code is transmission recording the problem but it sounds like the P0638 is causing the problem

 

Do you know where ISC actuator/throttle motor and APP sensor is located?

 

The problem was fixed.

 

can you tell me what the prob was please? my 05 has the same code