Got a CEL yesterday at 73k miles, Catalyst effieciency low bank 2, and the dealer gave me a new y-pipe with cats today. Got it back and it idles rougher. I have it tuned with the Diablosport Predator with my STS turbo kit. I was wondering if its getting less backpressure with the new cats and thats making it run rougher? I was also wondering if they flashed the computer back to stock would it run at all? It seems to be idling around 500-600 rpm. I can feel the truck shaking sitting at a light. It also had 3 miles extra on it from when I droped it off. I was thinking maybe they hot rodded it. My methanol switch was flipped off and it wasn't when I gave it to them. I was thinking if they did hot rod it I wanted the methanol on. Any inputs? If the motor is F'ed up how do I prove it was them?

 

to bad you didn't notice the 3 extra miles before you left that could have helped but i would imagine it is almost impossible to get them to take the blame if it is their fault