Dear Scotty - i had a po302 code on subaru impreza 2.5l engine. Plug boots were oily so replaced valve cover gasket s. New plugs and wires. Next morning started engine and smoke poured from exhaust. Smelled gassy. Drove car about 15 miles, and smoke stopped, but overheated. Car cooled down and I filled the radiator. Check eng light again with same code, no 9thers. Oil filler puffs out air, but no smoke. What should I do next?