Chevrolet: cylinder 4 is misfiring, chevy malibu, coil pack

Question
Hi I have been haveing a reccuring problem with my 2002 Chevy Malibu. The check engine light keeps coming on, and when I have it checked it says cylinder 4 is misfiring. I changed the plugs, wires, coil pack, erg valve, fuel pump, catalycic converter...everything was fine for a couple weeks then the check engine light(cylinder 4 is misfiring) came back on...it appears to be running fine but I am afraid that whatever is causing this will blow out the catalytic converter again...any ideas?
Thanks, Wes

Answer
You say it is running fine but it takes a really bad misfire a long time to actually damage the converter. The only thing that I can see from your list of parts that you didn't replace was the fuel injectors. You probably dont have a bad one, just a clogged one. You should take it in to the dealer. They will have the proper equipment there to test and clean the injectors.