2002 Saturn SL1 Service Engine soon Light code P0303

The things to remember is there is more then just a spark plug and wire that will cause a missifire. Low compression will but the way u describe ur problem doesnt sound like its that.A bad coil u could one of those though only acting up on certain conditions.A bad or clogged injector or a bad wire controling that injector. Aslo the driver in the ecm that controls the injector.U might have a bad coolant temp sensor those usually affect alll cyclinders but I have seen them do alot of weird things too. Those are some things u can check but u have to check them when there happening.I would cheeck the compression of all the cyclinders just to rule that off and be on the safe side. Also check fuel pressure and the fuel filter for restriction. Let me know what u find.