vacuum lines?
 

I was driving my car to drop off my gf to school and i stop'd at a stop light. and then all of a sudden my car just started to rev by itsself and then the CEL came on ... it would go to 1-3 rpm. I've had this problem before, but the car died everytime i started it. But this time its not dying. I just had the ECM replaced because thats what the dealer said it was the problem. I had it replaced like 1 or 2 weeks ago.

pop the hood and check for vaccuum leaks, and look at the idle air control valve