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Old 01-17-2002, 02:38 PM
Posts: n/a
Angry Engine doesn't shut off - vacuum problem

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.

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Old 01-17-2002, 04:13 PM
Registered User
Join Date: Dec 2001
Location: Las Vegas, NV
Posts: 56
I was changing glow plugs in my car and accidentally broke a nipple off of a connection on one of the vaccum lines. After that my car would not shut off. I just super glued the connection back together and it has been OK since. I plan to replace the brittle plastic connections. You might want to just check to see if any of your connections are cracked and leaking.

82 240D - 257k
84 300d - 86k
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Old 01-17-2002, 05:45 PM
Registered User
Join Date: Jan 2002
Location: Northern Calif
Posts: 116
There has been lots of discussion on this forum about vacuum problems...try a search.

If you are lucky, one of the lines may have been pulled off when the oil filter was last replaced...the lines going to the passenger compartment are nearby. You can disconnect the lock system lines by pulling them loose from the 1X2 check valve and plugging the check valve side. These lines are solid yellow and yellow with stripe. The solid yellow one goes to the driver side door lock valve, and the striped one goes to the accumulator tank (stores vacuum to allow several lock/unlock repititions). If the engine shutoff works, and the car is shifting ok with these lines plugged, the problem is in the locking system...likely one of the door actuators.
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Old 01-18-2002, 12:11 AM
Anthony Ryan
Posts: n/a

Yes I have the same problem in my 1980 300TD wagon. If I leave the heater on the car will not shut off. Very strange.
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Old 01-18-2002, 08:38 AM
84300DT's Avatar
Senior Member
Join Date: Jan 2002
Location: Mass.
Posts: 2,219
also had the same problem - make sure you check that
vacuum line to shutoff valve is on and the extender hose
is still good (its right next to the oil filter towards front of
car) sometimes replacing the small extender hose will help
as need a tight connection for the vacuum to activate
the shut off valve and turn the car off. On the other hand
it just mite ''self heal'' as happened to mine

ps: u can always manually turn the car off by pushing the
lever on the throttle linkage with the word 'stop' written all
over it - guess mb engineers knew the valve would fail sooner
or later!
1984 300D Turbo - 231k....totalled 11/30/07 RIP
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Old 01-18-2002, 10:11 AM
Registered User
Join Date: Sep 2001
Location: Concord, MA
Posts: 603
Sounds like an easy fix.

Since the engine shuts off when you lock the drivers door, and since the drivers door lock doesn't control the other doors, I believe you need to look at the vacuum lock switch in the drivers door....take off the interior panel and plastic and check it either have a vacuum fitting that has fallen off or is cracked (thats my guess), or you need a new switch...It is very obvious how this switch works when you see it.

Good luck

1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)
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Old 01-18-2002, 10:43 AM
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Thanks to all of you for the input. I'll dig into it tomorrow! I'm really glad I found this forum. Hopefully, I'll be able to help folks out myself down the road.

Appreciate it!
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Old 01-18-2002, 11:29 AM
jcd jcd is offline
village idiot
Join Date: Jun 2001
Location: Northern New Jersey
Posts: 1,102
Careful in the Cold

Given the age of the hoses & fittings in the vaccum system, I would be VERY careful working on these in the cold as they are very brittle and prone to breaking. This is also true with the plastic snaps that hold the door panel on.

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Old 01-18-2002, 12:43 PM
Anthony Ryan
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Rixter you're in Frederick MD eh? I went to school for a short time there when I was a lad. (Lived in a little nothing town called Buckeystown)

I remember frederick being what i thought an american town should be: Small and friendly, with mostly small family owned shops on the streets. Changed a lot I imagine tho.

Cheers mate

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