Have an 02 pontiac grand am with the 2.2l ecotec engine with approx 140k. Cylinder 3 misfire code comes up on the service engine soon light. I can hear the misfire while at idle, it is intermittent. I don't feel any loss of power. I have replaced the plugs, boots, switched coil pack and also hub, replaced the fuel injector and it still misfires. The compression in the cylinder is 180. Any idea why this is happening? I need to pass an etest and this is causing me some problems.