Twice, during the past 6 days, I stopped and parked my car and left the car for a few minutes to get something. When I came back and started the car initially the RPM's were around 1,000 but quickly went to zero unless I put my foot on the gas pedal. When I did not do this the RPM's went to 0 and the car stopped. I started the car again and the same thing happened. I left the car and went to make some phone calls for help and then came back to the car after about 15 minutes or so and started the car and everything was fine. No idle problem. What could be happending ?