David Dodge,

As Larry noted you do have the equipment for automatic door locks in your car, but also have a vacuum system leak that has rendered the door locking system non-functional. If you can manually draw a vacuum on the tube going to the shut off valve, and not get a mouth full of engine oil, you are probably not dealing with a bad shut off valve. As Larry noted, you probably have a vacuum system leak in the door system.

I disabled the door lock system on my 1982 240D when I suffered similar symptoms, as the door locks were deemed a less vital function than shutting the engine off. I cannot remember which tubes I plugged but it worked and I have not had another problem since. Since you will likely not miss the system if it continues to be non-functional, you may want to try this. I plugged the lines by screwing a slightly oversized screw into the tube and then covering it all with a few winds of electrical tape.

You might also test the key operated vacuum switch by hooking it all up as it was, and then taking the line that goes back to the vacuum system and routing that to inside of the car. Then, when you turn the key to the off position, you can suck on the line and if the car shuts down, the switch should be healthy.

Good luck, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)