I have a 2002 trans am, i have been having a issue with the motor throwing a misfire code (p0300) and a code for both my upstream O2 Sensors ... well i changed the spark plugs , spark plug wires , put in New O2 Sensors and checked the coil packs but for some odd reason it’s still throwing the same codes, what else could be causing the problem???

 

What are the codes? Any mods to the engine? 1st thing I would look for is vacuum leaks and look at the fuel trims.

 

+1 For checking for vacuum leaks. Special attention to the PCV hoses. They are old and worn out (most likely)