Suggestions
For a great example of a driving engine, you should try find Koala Clock's (Simon McClure's) CAR engine. It floats arround somewhere at clockcrewDotCoDotUkForwardslashSubliminal. You should be able to learn something from that.
Anyhow, a suggestion would be to make the car unable to turn when stationary. Last time I checked, cars didn't have a zero degree turning circle.
Let's see this implemented into a decent game now