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?