On that car, the resistance spec for the CPS is 680-1200 Ohms. Along with the fuel pump relay, OVP and ignition wires, that would be a good place to start some troubleshooting, and it couldn't be an easier DIY project. Can be done in less than 15 minutes.

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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