did your ecu get wet sometimes in the older cars water can find its way down there to the plugs. had a friend with a del sol that leaked when parked a certain way just dried the plugs and ecu with blow drier and it ran. also some store brand pumps just dont last long or even start right up when installed and have to go get another ive seen it happen but dont know why! also could be the muffler bearing or kanooter valve! lol jk!