The scangauge shows only the #2 cylinder misfiring, it comes and goes, it jumps from 0 - 72 and everywhere between. I changed the middle coil pack and all 6 plugs. Tried different gap settings, switched plug wires. Could a bad O2 be my problem? I don't think it's a chipped piston or a bad injector due to the fact that it will be great for 2-3 days at a time then come back.