i have a 97 Nissan Altima and it started skipping on November 13. I replaced the plugs, wires, cap, button, then i had a diagnostics run on it, the car had a crankshaft position sensor, knock sensor, and fuel filter, egr valve gasket, it still runs rough when at idle. runs fine at normal operating speed and rpm. i am replacing the egr valve next, i dont think that it would be the coil. you can hear it at the tail pipe skipping, then i had the diagnostics test again and it had a number 4 cylinder missfire. i am lost and don't know what to do now.