Hello everyone, I'm new here so this may not be the best place to post this but it seemed fitting. I've have a 98 grand prix gtp, all stock, no mods. I keep getting a p0304 cylinder 4 misfire. Now before we jump through the usual hoops, let me explain. The light will only come on if I let the car idle for 10 minutes or more. If I start it up and leave immediately I can drive the entire day without the code returning, once it comes on it stays one until erased. It does not affect the performance of the vehicle I average 19.6 mpg as it always has and it runs smooth under load and otherwise. I have been through the usual suspects. I have replaced the coil packs, spark plugs, plug wires, I've replaced the fuel injectors as well, yes they were flow matched and all the parts are original GM parts. I have also replaced the lower intake gaskets with the zzp aluminum ones, I am getting very good compression on all cylinders and I've replaced all the engine/transmission mounts. Light still comes on, super annoying to look at lol. What am I missing here that could be doing this. I have a stage 2 zzp performance kit ready to go on this vehicle but I would like to track down this issue first.
