I have a '97 4.6 that started to idle rough yesterday. The check engine light came on and flashed, an auto zone OBD check said the #7 was misfirring. I pulled the plug and it had some rust colored corrosion on the wire end, and inside the boot was all corroded too. I changed all the plugs and wires about a year ago, and the other plugs and boots look fine. I tried a new plug and it generates a spark, but does that necessarily rule out a bad wire? I want to check all the simple fixes first before i take it to a shop...

 

You have water getting into that spark plug hole. Look for a leaking coolant hose. I would replace the plug and wire before you take it to a shop and pay all that extra money.