I replaced the plugs, wires, dist cap, and rotor about a month ago. This past weekend, I noticed a heavy miss while under load. I asked the service manager at the dealer to check what codes it was throwing while driving. It was the #3 cylinder misfire. I pulled the spark plug and it had some heavy buildup on it. Like, stuff I had to use a screwdriver to chip off. I cleaned it up, and I don't feel the miss anymore, but I have to think that this is going to happen again. I replaced the coil this afternoon just for Sh!ts. What could be causing the #3 cylinder to continue to foul?