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Old 10-25-2005, 01:40 PM
Posts: n/a
Vacuum experts help!

I have an '85 300D that I'm trying (quite unsuccessfully) to fix... the problem is the common "engine won't shut off with ignition."

I put a vacuum directly on the switchoff valve on the IP and the engine wouldn't shut off, so I replaced the valve with the valve off of a parts car (I tested it before install - a simple suck on the vacuum fitting retracted the arm quite easily).

After replacing the valve, I put vacuum directly on it, but it didn't shut off. I figured that I missed the linkage when it was installed. I pulled the valve and reinstalled it, checking for the link. I was pretty sure I had it... but again, it didn't work. I went through the hassle of pulling it out, testing it again, and reinstalling it - sure this time that I grabbed the linkage. Still no shutoff...

Is there anything else that might be wrong here?

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Old 10-25-2005, 02:48 PM
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
It does not appear to be a vacuum problem. You are applying vacuum to a know good actuator and it won't shut the engine off.

What is the condition of the actuator that was removed? Does it properly function, or has it failed due to to an internal leak? If the old diaphragm is faulty, then you can be reasonably sure that you are not installing the new one correctly.

If the old diaphragm works in similar manner to the new one, then there might be an internal issue with the IP, but, I've never heard of this.
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Old 10-25-2005, 03:11 PM
Registered User
Join Date: Dec 2002
Location: RI shore
Posts: 2,937
Is this a vehicle new to you? has someone monkeyed with the external throttle linkage in such a way as to restrict movement of it?
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.
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Old 10-25-2005, 03:14 PM
Registered User
Join Date: Jul 2004
Location: Norwich, VT USA
Posts: 905
could there be a leak on the "new" shut of component that allows movement of the actuator rod under no load but once its trying to pull on the IP (ie installed) it doesn't have enough pull?
Rob M
Norwich, VT USA
1980 240D Euro delivery 4 speed manual silver/blue
~160K miles
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Old 10-25-2005, 03:44 PM
Posts: n/a
The old valve had a bunch o' stick in it... It was resistant to compression by hand and by suction was tough. I have no idea if I'm installing this thing right. In other threads, people have mentioned snagging another linkage within the IP (?). I know that the valve arm is pulling on something. There is so little work room there that it is difficult to imagine it having to be more finesse than I have been able to manage (in the process I have felt it when it is seated but NOT pulling on a linkage).

The vehicle is new to me... I'm not sure about any one monkeying around with the throttle linkage. I initially thought that this might be a problem because the linkages weren't releasing very well. I lubed the linkages atop the valve cover and they seemed to move a bit better. I thought I read somewhere that the external linkages do not affect the shutoff valve.

A couple of times since the install (it has only idled in a garage - it hasn't been driven anywhere), the car shutoff (not consistently) after a 15-20 second delay. I haven't been able to duplicate this since. I guessed that there was some leaking going on in peripheral lines/fittings that I plan to replace. I then moved to isolating the switchoff... in my mind, it makes sense that putting vacuum directly on the valve would cause shudown, since that is what the ignition switch does.

I guess a leak in the newer valve is possible but not probable. It seemed pretty functional.
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Old 10-25-2005, 04:54 PM
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smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,800
It's one thing for the shut-off valve to react to a vacuum signal. It should also hold vacuum for a few minutes at least. Check an engine with a functioning shut-off valve. After you pull the key and lift the hood the stop lever will still be down.

87 300SDL
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Old 10-25-2005, 09:50 PM
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Join Date: Oct 2005
Location: Southport, NC 28461
Posts: 22
Ken in NC

While it is not a 300D, my '82 240D has two vacumn lines coming from the key switch, both going to the IP valve. These small lines are hard brown plastic, and pass through the firewall near the steering shaft.

I know that the engine will not shut off with the key when the lower line is disconnected, because I accidentally pulled the lower line loose when removing the top of the oil filter housing

You may want to verify that you have both brown lines connected to the IP would be easy to accidentally pull one loose and not notice it

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