When turning key off engine goes into very low idle (barely running) instead of turning off, I have to stall car with clutch in gear.

I figure there is some sort of turn-off solenoid on the injection pump? What is it exactly called? Replacement difficult?

Thanks,
John

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1986 190D, 2.5L, 5-speed swap, 180,000 Miles (60K by me).
Jeep CJ-7 with Cummins 4BT/NV4500/AtlastII 4.3.
Grand Wagoneer 4BT project in progress!

Not familiar with the 2.5l but I'm pretty sure it has a vacuum shut off. You probably have low vacuum either because there is a bad diaphragm in the shut off valve, a leak in the system, or a problem with the vacuum pump. You'll need a Mity Vac to diagnose the problem. Alternatively, disconnect the vacuum line going to the shut off and suck on it hard a few times. If the engine shuts off promptly, you know the problem is in the vacuum system somewhere and not a bad shut off diaphragm.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

You have A shut off Valve Problem. It is Above the Injection Pump It cost around $45.00.

Only if it needs to be replaced. Most likely its just a broken or dislodged vacuum hose.

I think your car has an electronic idle control like my '87. When the key is turned off, this device loses its power and the engine is left with only the mechanical idle setting of the IP, around 500 RPM. That's why the engine continues to run "barely." As the others have said, the no-stop problem is most likely a vacuum leak or fallen-off hose. Failure of the shut-off valve itself is less likely but possible. Eliminate any vacuum leaks first.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

my '95 606 has a plastic shut off valve - mine cracked and I was able to repair it carefully with some JB weld using a brakeclean spray tube to hold the plug centered on the housing while the JB cured.

Check the vacuum tubing leading to the shut off valve for any cracks / holes.

If you have a mightyvac - see if you can operate the shut off valve with it to see if the valve is in fact operating properly or not.

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95 E300 Diesel 265k and counting