I too had engine shutoff problems, and upon shutdown, the engine would almost shut off, but not completely. So, it would sputter for a little while.

Anyway, I found the vacuum leak in the hose leading to the rear head-rest releases. That was located under the rear seat !

My friends don't let me forget that one ... engine would not turn off, and fix was located under the rear seat !

- michael

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Michael H
1986 300D W124 5-spd manual 250k miles