I just changed the oil in my 1982 300D Turbo, and ran into a problem. I turned the ignition on ran the car for awhile, and tried to turn the car off, but the engine kept on idling. I opened the hood and hit the fuel cut off and the engine stopped. Every time I drive my car I have to pop the hood and turn the engine off with that switch. Any ideas whats going on here? Hopefully electrical, and not something like damaged pistons.