This is going to sound crazy...but make sure your vent line on the valve cover isn't plugged up. Positive pressure in the crankcase will act on the shutoff solenoid and reduce or cut off fuel depending on the severity. I went through that years ago on my W116 and it took a LONG time to figure out.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche