The other day I filled my dads conti up with sunoco 94 ontop of the about 1/4 tank alreay in there of sunoco 93 (different station). When i go home the car was running fine and i hit reset on the milage and turned the car off. When he went to turn it on a couple hours later it turned on and immediatly off again. Then when he got it turned over it was idling very rough he said. I checked it today and it was a bit rough but not too bad. The plugs and wires have probably only 5-7k miles on them at most and the car has had fuel system cleaner and seafoam done recently. It only has about 85k miles on it. What could cause something like that so suddenly when an hour before it was fine?

anything is possible. could have a plug laying down.

huh, do you mean a bad plug?

lux before you get to involved in diagnosing it check the service engine light.if on go to autozone and have them pull your codes (its free)or if you have an obdii scanner do it yourself.no light or codes then pull your negative cable for a few minutes,this will reset the car and it will have to relearn its idle.let the car idle for at least ten minutes then go drive in town stop and go for ten minutes or so then hit the highway again for ten min or so.this will allow the car to relearn its idle.if after this it is still rough then we can try and help you diagnose the problem.good luck
john :L