so i just finished a massive job, taken me 5 months. root cause was head gasket failure after not fixing minor coolant leaks. lessons learned. took the opportunity to get the heads flattened 0.003, valve seats machined, new seals, pressure tested, no cracks. put on headers, bilsteins, CAI, new wires, plugs, front O2 sensors, supercharged X radiator (mines a 2001). yada yada yada. i got tons of advice and tips after this job. feel like i could take this thing apart with my eyes closed now. #6 spark plug, no problem. anyways, I'm getting p0304. no other cylinders. i got spark outside of the cylinder. runs intermittently fine. always idles rough. It's only cylinder 4. no vacuum leaks i could find. if it was air i feel like it would show up in other cylinders. Its getting fuel. when i pulled the plug there was fuel all over it. cleaned it, checked for spark. confirmed. tomorrow I'm going to swap plugs and wires with other cylinders and see if i can narrow it down to a specific connection. i did not replace the distributor, or cap. I don't plan on replacing things until it magically goes away. I'd rather confirm the problem first. anyone have any tips or tricks? I feel like I'm on the right path, but looking for sage advice from the crowd. oh i should also mention it had a quarter tank of very old gas. I filled it with premium, and have already drive on the highway for about 30 minutes, so it should have met the 10minutes at 3,000rpm or whatever it is to relearn the air/fuel mixture.