Sometime it dies sitting in idle, sometimes it shuts down driving down the road. I can start it right back up, but then it will die again. Sometimes it has done it several times, then it runs fine. I have a 25 mile ride to school, it died 6 times on the way, then made it the rest of the way fine, and back home fine. Sometimes after it starts back up it backfires...not all the time. Thoughts?