I have a 02 Trans AM with NGK TR55 set the gap at .50 she ran to rich and then set the gap to .40 started to misfire gave me check engine light both times when set to .40 gap got P0300 and when set to .50 got like 3 codes P0140,P1133,P0160 Just wondering where the gap should be set at. It have bolt ons Header, Exhaust, Air lid, KN filter Stall 2800 342 gears

 

I never adjust them unless they're off - just check them. I think they're supposed to be .055 from the factory.