For a while now it has been taking longer and longer for the engine to stop after turning off the key. At first it was 10 seconds, then 20 and now it just keeps on running at less than idle speed until I put the Transmission in gear to stall it.

I have pulled a vacuum on the shut-off valve on top of the IP with my trusty MittyVac and it stops immediately (Stop lever moves down also). There is no sign of oil in the vac line to indicate a leaking diaphram.

I then disconnected the Brown Vacuum line that Tee's off the Big Black Brake booster hose and goes (I think) to the Key Switch and pulled a vacuum there with the key in the 'off' position and again the Stop lever moved down straight away.

This seems to indicate that both the Shut-Off Valve and Key Switch Valve are working correctly, so what else might be the problem

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown

How's the vacuum from the pump? Any other leak under hood? Tee a gage into the line and watch it as soon as you turn the key off.

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'82 300SD - 361K mi - "Blue"

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

listen, look, .........and duck.

Replaced the Vac Pump last winter so it should be good.

All other Vacuum systems seem to be working OK, Door Locks, ACC, Brakes.

I will try hooking up the Vac. Gauge to the lines and see what happens.

[QUOTE=Dervman]Replaced the Vac Pump last winter so it should be good.

All other Vacuum systems seem to be working OK, Door Locks, ACC, Brakes.

I will try hooking up the Vac. Gauge to the lines and see what happens.[/QUOTE=Benz*Girl]
My 76' 300D vacume line comes apart at the same spot once in a while, I just replace the ends and It shuts off pretty easy. The STOP button is probablly more healthy than using the transmission to stop er'.

Connected Gauge and all main Vacuum systems look fine, although there is something weird going on with the Shut-Off line at the valve on the IP. I thought it might be leaking a bit so I replaced the rubber hose between the nylon vacuum line and the valve. Same thing is happening so either I have two leaky hoses or the Shut-off valve is leaking slightly.

If I connect the MittyVac to the hose connection to the valve it will shut down the engine but when stopping with the Key Switch I noticed that the Stop Lever seems to move almost all the way down then come back up a bit while the engine keeps running. Maybe the MittyVac has a strong enough initial vacuum to pull the stop lever all the way down to stop the engine, but not the key switch vacuum line.

I will investigate some more in the morning.

You seem to be on the right track.

Perform a leakdown test of the shutoff diaphragm. With the engine off, pump up the vacuum to the diaphragm and see if it holds vacuum for 30 seconds or so. It might shut the engine off with the Mityvac, but, if the diaphragm is leaking slightly, the amount of air movement from the key switch might not be sufficient to shut the engine down.

I had exactly the same problem last week, tee'd into the line and discovered very little vacuum. The valve was leaking just enough that there was insufficient volume of vacuum to overcome the loss even though the mity would shut it down with no problem.

Good luck,
Jim

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2005 C240 4matic wagon (daily driver)
87 190D - 225K (on loan)
85 190D - 312K (on loan)
2011 Subaru Legacy AWD (Wife's)

99.9% sure I have found the problem.
Re-checked vacuum system and all was OK except I noticed that after pulling a vacuum on the Shut-off valve the engine would stop but there was a slow leak-down and the Stop Lever moved part way upwards. Tried the same thing on the line to the Key Switch and the lever moved down but never travelled to the full STOP position.

A new Shut-off Valve & Seal is on order.
Thanks for all the help and guidance.

1976 300D, 115/114 body style.
I've been reading the posting on this subject. I had my steering column removed and with it the two vacuum hoses that attach to the key switch.
A couple of questions and my assumed understanding of the entire vacuum/stopping idea.
If I understand the discussions, the IP is "Stopped" by applying a vacuum to the hose that goes to the back of the IP (small cylindrical object at the direct end of the IP) This vacuum is generated by the vacuum pump in front of the IP (driven by the timing chain) and the generated vacuum is stored in the multi-bladder storage unit located inside the drivers front fender, behind the wheel/mud guard plate. When the key switch is placed in the stop position it sends some of the vacuum to the cylinder attached to the IP and pulls the rack to 0, or No Fuel. Is this correct.

I ask because I have deleted all of the vacuum door locks and the trunk and petrol fill cap lock. I have replaced them with electricial units for remote operation. I am still using the vacuum and the lines to operate the heater & A/C vent switching system. In having the vacuum lines rerouted slightly, I am questioning if it matters as to which hose goes to which hose barb on the key switch. In my rerouting I have one of the vacuum hoses coming directly from the large black hose (using a T fitting) to one hose on the key switch and the other hose goes to the IP from the key switch, would this arrangement "Stop" the engine when turned to OFF. I am not sure as to which barb that each hose goes to, it sounds like it just connects the two port of each barbed connection together.

I have a few other questions, but will await a reply to this specific problem. Thank you for the interest and any response.

I read your post while looking for solutions to my problem; which is that if I have the door locks in the open position while driving, the engine won't quit. If I have the door locks in the locked position, all door buttons/locks are down and the engine stops when I shut it off. I've checked the vacuum pump and it's fine and I've gone through all the doors checking for breaks in the yellow tubes and evaluating the diaphram switches, and all seem fine (as far as I can tell). I even replaced the RR door diaphram switch because it seemed suspicious but that wasn't the problem. I checked the fuel flap lock, which looked fine but which I bypassed after having too much difficulty reattaching. I'm at the point of bypassing the door lock system and manually locking the doors like in the old days.
You wrote that you replaced the door locks with an electrical system. Can you describe to me how you did that and where you got the electrical switches?
Thanks,
Ralph

I purchased the standard style (universal) of remote operated, gear driven door locks from a stereo store in seattle called CARTOYS, cost about $20.00, but my son found some just like mine (cheap knock-offs) on e-bay for $3.00 each, pays to shop around! The electrical operator is 12v and takes the place of the vacuum operated switches. I had to custom make simple brackest that hold each door operator in position. I placed a 2 terminal connection strip at the approximate location as the old vacuum lines. Just anywhere I had room. The two wires were ran to the remote control operating unit. So when I want the doors opened it acts just like any other remote operated door lock system. One of the doors needed to have an additional 90 degree bellcrank installed to orient the operator in the proper direction. If interesed I could send some photos.

I had also designed and fabricated a remote trunk release for the same car. I removed the two coil springs and replaced them with "hatchback shocks" and brackets that hold the "shocks" directly between the channel of each trunk hinge. When I operate my custom made trunk release, the two "shocks" automatically open the trunk to its full position and hold it in that position. The custom made latch release still allows the trunk to be locked or operated with the key, aka by hand. The design employs the use of a small roller bearing machined into a 1/2 inch shaft that rides on two bronze flange bushings. The electrical operator is from a caddy trunk relase solenoid. I just used the solenoid section only. The entire assy sets in the trunk lid out of sight in the cavity. I did need to modify the lid latch by drilling a hole to accept the bearing/shaft assembly so when it actuated it would push the latch lever off of the trunk lid latch. Quite a bit of theory and tinkering with different types of push/pull sytems were tried.

One other item I fabricated and installed was a limit switch for the two front windows. I noticed that the window regulators were easily cracked, aluminum frame, when the window was rolled up. If someone kept applying the power to the window it would over stress the regulator and crack the regulator frame. I breadboard designed a latch/reversing relay set with two adjustable microswitchs that stop the power from continuing after the window has reached its full up or down position, Both micro-switchs are adjustable with just the door skin removed from the door.

I seem to have nothing but time to devote to trival things that I think could be better, Plus this is the first car I have performed a ground up restoration. I even learned how to sew and installed a completly new interior, PLUS put a twin seam vinyl top on the car, that should set it apart!!!

Seeing pictures of your electronic replacement switches for the original vacuum switches would be helpful, if you don't mind. I'm impressed with what you've accomplished with your renovations.

Ill try to get some photos together within the next few days. I can either send them to you directly or attempt to post them to this site. I still have some learning to do as to the procedure for postng photos, thou!

Yes, it does matter. When you turn the switch on, it opens the IP line to the atmosphere to release the vacuum, and blocks the supply line to prevent a vacuum leak.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

Yes I understood that was the way that it operated. I want to know if it matters which hose (vacuum hose from tank or hose from IP) that goes to which barb on the key. As you say when the key is in the RUN position, there is no vacuum going to the IP. When the key is placed in the OFF position it interconnects the vacuum tank/line to the IP to pull it to the STOP position. So which hose barb on the key switch does the IP hose connect to and which hose barb does the vacuum tank connect to? I would hate to take the key assembly out, AGAIN ,just to determine which of the barbs to connect. I suppose that I could remove the dash pod and use a small jumper hose to apply vacuum and operate the key to determine, yet surely someone knows which is which.