2007 jetta, 2.5L. Owned since new, and it's done this for as long as I can remember. If I start the car from a completely cold state, and then shut it down again quickly (like backing out of the garage and parking in the driveway, etc.) the engine will keep running even after I take the key out. It will run on its own for 5-10 seconds at least. This only happens when the car is completely cold and only run for a very very brief period. No other issues whatsoever. Has anyone else experienced this?