I have an 07 Impala SS with 78k. Thursday I filled my tank and drove around to run errands. Everything was fine. On Friday (about 40 miles after the fill up) my cel came on along with service traction control followed by a very rough idle and hard shift. The cel code was p0304 which is a cylinder 4 misfire. Prior to that I had no lights for the going on 3 weeks I've owned the car. I replaced the plug in cylinder 4. No luck. I swapped coils and wires from 2 different cylinders. No luck. I've researched and all the posts I've read end with a trip to the dealership.
