My friend filled his almost empty gas tank on his '99 Camry 4cyl 2.2 and went about 1/2 block and engine started missing. He suspects bad gas. I don't think so because the miss is so constant and only seems to miss under load. I also doubt (although possible) that the potentially bad gas would have got into the engine in 1/2 block.
3 weeks prior to that he left the oil cap off and threw oil around the engine compartment. That meant it got on the fuel injector wiring loom and spark plug wires.
I pulled codes PO300 (#3 missfire), PO302(#2 missfire), PO303(random missfire). Does this mean it has to be electrical and not fuel? I put my timing light on all 4 spark plug wires and with engine under load and missing noticed the #1 & #4 seemed to fire evenly and #2  skipped lighting once and awhile, #3 being the worst. Also there is a small backfire, popping when it does miss.
Cleaned engine. Spark plugs and spark plug wires are fairly new and look clean and not at all oil soaked. Checked under the spark plug covers and there was no oil or water in those 6 inch deep spark plug holes. The coils did not get oiled. But I noticed #3 and #2 come off the same coil and I am suspicious of the coil but do not know how to check it with my primitive tools.
He added a bottle of Chevron Techroline just for good measure.