i have a 2000 chevy silverado 1500 and about once a week i will try to start it and it will turn over and start for a split second and die. then i will let it sit for about 20 min and it will start and run just fine for another week. but it seems if i turn the heater a/c fan off before i start it, it wont do it but sometimes i forget and im sick of it! any suggestions?