I have an 04 impala ss, I'm getting a misfire on cylinder number 4. runs rough, MIL light will come on steady if driven slowly or around town, but if I drive it hard, the miss goes away temporally and it will drive low speeds fine for a while. (I have a scanner and can see the missfires when they happen.) I replaced plug even though it looked good and gap was .060, also replaced plug wire because it broke pulling it off. Ohm'ed all injectors, (11.5-11.7), put a noid light on the injector leads and all looked normal, swapped coil packs and still have cylinder 4 misfire, I sprayed starter fluid around intake, no change in idle, swapped out the ignition module with a known good one, then even swapped out the injector with a known good one. Same f$#king thing, cylinder 4 misfire, unless I beat on it. I do notice a slight exhaust leak on the tube for the egr, but its almost undeteckable until you rev it. Any thoughts????