Engine Performance problem
2004 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic 79000 miles
I have a 04 GrandPrix GTP with a supercharged 3.8
i was going to put a smaller supercharger pulley on it to gain more boost. But I heard that wasnt a good idea yet. People said I didnt have supporting modifications less restrictive exhaust, intake, rockers, etc etc. Well the car always had an annoying little miss at idle every now and then. Very slight, but annoying. So I took it into my own hands to do a tune up air filter, pcv, c(not the fuel filter though)oilpacks, wires, and colder NGK TR6 plugs ( a supporting modification for the future pulley I have laying around. The car ran ok for a few days, then every now and then when I would really get into the gas the car would " bog" misfire just break up really badly. But only everynow and then not all the time. I couldnt figure it out. Then I pulled a p0420 catalyst code. The cat was clogged up took it in warranty replaced it and the car ran better than it ever has in the year that I have owned it. The misfire wheni would get into the gas was gone as far as I could tell! Then a few days later I put on a K& N cold air intake. No leaks everything is beautiful with the new cat and intake the car is running very strong! Two days after I put it on im driving it I start to get in the gas to pass someone in traffic the car starts misfiring like it used to. Then by the end of the day the engine light is on again! Im hoping and guessing its the colder spark plugs? Or maybe its just to cold to have that intake on with cold plugs like that right now?