I wonder if you ever had a new cambelt in the engine. That's the symptom when a worn belt jumps timing a few teeth. The next few teeth it jumps will damage the engine seriously. Have it checked soon. A timing light will show the ignition timing quite a bit off, but do not try to adjust that- it just shows that you needs to have work done. You might spend $200 for a new belt being installed. If there are other parts behind the cam belt, like some cars have their water pumps back there, don't miss the opportunity to have those things replaced now rather than pay later to go in the same place for additional repair- and additional cost.