... 87 300D doesn't shut off when I turn the key to "0" position. I shut off the engine manually, and am assuming I can do this and still successfully start up and drive again (either that or I'll be in trouble when I go to leave work at 2 am). I'm taking it into the mechanic to have it looked at on Wed. Just so I'm not completely ignorant to what's happening to my car, could someone debrief me as to why this is happening? He mentioned that it may be a vaccuum failure.

Feeling very frustrated at my lack of knowledge ...

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

The vacuum shutoff switch could have gone bad, or the vacuum seals in the ignition switch, or a leak somewhere could be making it so there's not enough vacuum to shut off the car with the shutoff valve....its got to be one of those things.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

It's a vacuum failure all right.

The least costly scenario, and the most likely, is a vacuum leak in a hose or a connector that prevents the ignition switch from getting vacuum.

If the switch gets vacuum, then either the switch is bad or the shut-off diaphragm on the IP is bad. The mechanic can easily confirm whether the shut-off diaphragm is bad by connecting a Mityvac to the shut-off diaphragm and attempting to shut the engine down with the Mityvac. If he can shut it down with the Mityvac, then the shut-off diaphragm is fine.

The last culprit, and most expensive, is the ignition switch itself.

If you need an ignition switch vacuum shut-off valve then you can have mine. I replaced mine thinking that's what was keeping my car from starting when instead I need the shut-off valve at the IP. I wasn't very good with hand vacuum pumps then but I can bet my life on it that next time I'll be a lot more sure before I try taking all that stuff apart again to replace that stupid thing. Let me know if you need anything. you can have mine for free if you need it.

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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Thanks ... I'll let you know what the prognosis is after I take it to the mechanic. I don't have the skill to figure it out on my own, so the mechanic is a safer bet. This will be my first repair with the new mechanic, so I'll have to cross my fingers that he's as reliable as the guy I had in my old hometown.

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

Check the following thread. Your shut-down valve is the culprit ... quite common maintenance issue. This is one you can easily do yourself for the price of a $45 shut-down valve and a six-pack!

http://www.peachparts.com/shopforum/showthread.php?t=119417