If you have not already done a search, there are many threads on this topic here. What you will find is that the list of possible suspects is long: accumulator, check valves, OVP, fuel pump relay, EHA, temp sensor, pressure regulator, leaking injectors, and more. Get hold of the FSM and start doing the troubleshooting tests. Most of them are easily performed, requiring only a multi-meter and common tools. Good luck.

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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