My 190D stutters for about 7 seconds before it dies, after I shutoff the key.
A friend watched the manual lever on the IP while I shut off the key, and the shutoff lever slowly moves downward until the engine dies.
I put a vaccum pump on the SOA holds vacuum. I put a smoke machine on the vacuum line going into the SOA, but did not see any smoke anywhere, even under the hood.
All other vacuum operated mechanisms work fine.
I have a Service Manual but it is only for Chassis and Body, and it doesnt tell me much.
I am hoping that someone can help me narrow this down some before I throw money away and waste a lot of time tearing things apart.
Does anyone have any ideas that may help narrow things down for me??

If you attach your vacuum pump directly to shut-off valve and apply vacuum, does the engine immediately shut off? If not, then the valve is bad.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

yes -When I apply vacuum to the SOA, the engine shuts off. (Sorry, I forgot to mention that).

For others. There is the shutoff valve on the fuel injection pump, the shutoff valve on the steering colum lock, vacuum leaks elsewhere in the system and the vacuum pump/check valve that can all have a hand in a slow or no shut off. Or any of the rubber connectors on the plastic vacuum lines.

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84 300D, 82 Volvo 244Gl Diesel

Certainly seems like there is a leak somewhere in the system. Keep checking and isolating parts of the vacuum system...should find it eventually.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Thanks for the feedback. I will have to look more diligently.