I have a 1997 Catera and today the while driving the car started running rough and the check engine light came on. I went to the auto parts store and used their computer to see the code and it read P0304: Cylinder 4 misfire. I pulled the sparkplug for the cylinder labeled "4" on the spark plug wire and checked for spark when the engine was running and it sparked. Also, it seems the car runs fine when I start it cold and leave my driveway but after about a minute it starts misfiring again. I recently replaced the coil pack and only #4 is misifiring, and if it was the coil pack, #1 would also misfire, so I don't think that is it. Any help would be greatly appreciated. Thank you.