Have a P0302 code come up on Saturday, misfired for about 20 minutes, then ok; SES light stayed on all weekend, without a miss. Started it today at noon, misfire all the way home & back, intermittent, worse under heavier throttle. Friend mechanic with scanner read code, #2 misfire. Changed plugs 2000 miles ago. Put dielectric compound on all plug terminals. I think maybe not enough dielectric lube. Pulled off that plug cap, quick visual inspection, frigged with it when putting it back on, to clean terminal. Also pulled #2 injector plug off of injector, check for corrosion, etc, ok. Put back on, cleared code, no miss. No code. Just before doing this, we could make it miss on demand with park brake on and a bit of throttle, was even misfiring when giving a good poke of fuel in Park.
My advice, clean (or replace) wires and terminals, put LOTS of dielectric lube in terminals and put some in every connection you can get it into. Will follow my own advice very, very soon.