85 300td shut off issue
 

Engine stops, although very slowly, when I remove the key and the doors are locked. Otherwise I have to hit the stop lever. This issue came on all of a sudden. I can't even get it to shut off even when I put the mityvac on the vacuum control valve. All connections are still good and rubber connectors are only a couple of years old.

Does this sound like a leak in the door locks somewhere or is the vcv shot?

Try using the mityvac on the shutoff valve itself.

If it shuts off properly then you have a leak somewhere. I would not suspect the vcv as the main suspect. If it shuts off with the doors locked then that suggests the leak is in the doors vacuum system.

Same thing happened to me. I isolated the AC (Green Line) and it stopped.