I have a 2002 pontiac Grand Prix GPT about 64000 miles on it and about every time you get on it it starts to miss the 1ST time replaced a coil pack and it seemed to be fine the 2ND time i replaced plugs and wires and it seemed to be fine again the 3RD time i replaced the same coil pack witch is the middle pack that is cylinder 3 - 6 but this time It still missing also it has been hooked up to a tester and it has a code of p303 or po303 need to find out what is the real problem???? Could it be a plugged injector ??? The car also has no catalac converter
