The car would run fine and then i would stop to pick something up and the car just would not start again. I would sit there for hours and nothing would change. The engine turns over and sounds like it is going to start but just doesn't catch at the end. Pop starting and jump starting have no effect. A day or 2 later when I go to tow the car it will start right up and run fine for an unspecified amount of time. I have replaced the spark plugs and air filter. Any help would be so very welcome.