I own a 1984 300D, and recently, the engine has continued to run after removing the key. I accidently found out that if I remove the key and then lock the driver's door, the engine will kill itself. I've also noticed (concurrently) that the driver's lock no longer controls the rest of the locks in the car. I know that the locks are pneumatic, and I'm guessing there's some kind of air-operated fuel cut-off valve that normally closes when the key is turned to off.

Has any one had this problem? What did you do to rectify? I'm planning to poke around in the car this weekend, but if someone can give me a starting point other than the door locks, I'd certainly appreciate it.