So, I bought this car a couple weeks ago from a private seller. 123,000 miles on it. Ran and driver perfectly....until the next day. Check engine light came on and then started blinking. But car ran and driver perfectly still. Took to mechanic....they could not find anything wrong with the car at all. So I just kept driving. Yesterday I accidently almost ran it out of gas. Right after I put gas in, it started idling at 2,000 rpms. When clutch is pushed in car jumps rpms. When any gear is engaged it runs fine. Thought maybe picked up some grit, so I ran a bottle of heat through it. It returned to normal rpms almost immediatly. However, when I hit quarter of a tank of gas the next day (today) it jumped back up in rpms and is doing the same thing again. Filled tank back up and added another bottle of Heat, no change this time. Any ideas?????