another misfire?

I had a random misfire a month or so ago... cleared the code, didnt think much of it... but it just happened again. both times i was driving to or from school, bout a 6 hour trip. I'm just wondering if anybody has an suggestions. I was thinkin maybe a bad plug, but it works fine most of the time with just isolated misfires.

Ideas? thx guys.

Did you pull the code to see which cylinder is misfiring. It could be a plug but wires are usually the biggest cause. If you haven't changed them lately you may want to try a new set. Coils can also be an issue but they will usually misfire on more than one cylinder since each coil is responsible for two. Finally there is a possibility of a dirty or defective injector. Not likely but can happen. Pulling the code will give you an idea on where to start.