I have a similar problem as yours. I changed the FD and it did not help. When I checked the fuel pressure it was 130PSI because my return fuel line was blocked and the pump was shutting down which caused the engine to die. After unblocking the fuel return line the car runs perfectly. My 280SL has not been driven for 5 years and this caused the problem.
Good luck.

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Roman
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87 300SDL 152K
86 420SEL 228K
83 280SL 145K (5 spd)
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