Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
I've heard of drive belt issues causing phantom misfire codes - the belt slips on the crank and causes abnormal changes in crank speed. I've never see it, but I've been told the best way to eliminate this is to remove the belt and recheck for misfires.
