I just purchased this vehicle and was out driving it to make sure everything was okay before giving it to my teen. After I drove it for about 1 hour it began to run rough. It stalled at an intersection, started right back up, but when I put it in gear it stalled, and would not stay running. I started it over and over, but as soon as I put it into gear, it stalls. After it cooled off, overnight, it started and went right into gear. What is this?