My check engine light indicates misfire in cylinder 2. car shakes when idling only.?

I have a 1997 mercury mountaineer 5.0 liter v8 engine the vehicle is idling rough when I'm stoped in all gears but neutral. It over heated a couple days ago 6/18/11 due to a busted radiator. I was driving on the freeway and of course car overheated and stalled out when I got it home I realilze there was oil that had spilled out of the oil dipstick and got all over the headers I finally replace the radiator new with new hoses and fasterners the cars engine light was still on got a diagnostics test saying misfiring in cylinder 2 and oxygen sensor error I inspected second cylinder to find there was residue all around the sparkplug looked like oil I took the sparkplug off to find oily residue on the sparkplug so I replaced the sparkplug with Ford oem part autolite double platinum just like the rest of the sparkplugs and install a new wire for that spark plug inspected the distributor caps clean and error free I have also replaced fuel filter with a wix racing filter change the oil and oil filter new air filter so I'm running out of thing but the engine I have a hunch suspecting that it might be a warped cylinder causing the misfire. If you guys can help at all in wondering what it might be and an estimated figure of how much it might be? I would greatly appreciate it Thank you