Well, from your list of repairs made and without knowing the maintenance history of the car, the obvious suggestion is a tuneup: plugs, wires, cap/rotor, air and fuel filters. After that, fuel pressure/volume testing to see what's going on with the fuel system.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't