So I just bought my first WRX ever and I was super excited. I bought it in Oregon and the only aftermarket done to the car is HKS HP cat-back exhaust.
The check engine light came on after driving it for three hours getting it home. Took it to dealer and they game me P0420(Catalyst System Efficiency Below Threshold )
The second code was P301(cylinder 1 misfire)
I had all new Platinum NGK plugs installed and the ECU was reset. Picked up car and it was fine for a day. Today was driving and the light came on again. Not sure what to do. The codes are back. Any help would be good. I have never been on a forum other than school. Please help and advise. The car is 2005 with only 38K miles and clean as a whissle. HELP