I have a 2002 WRX with cobb stage 2, helix up/dn pipe, & AEM ram air. I am getting P0304, whixh from doing a search means that there is a misfire in cylinder 4. But while the car is on it blinks which I have heard could also be detonation. How should i go about fixing the problem? Should I hit "reset ECU" on the cobb unit or take of the battery and do a hard reset? Should I get new spark plugs? (if so which kind do I buy) Or what?