I havea 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 orbad fuel at bottom of fuel tank since it was almost empty. Please help!

 

The problem was fixed.