It sounds like the OVP relay to me- do a search on OVP. You will see what I mean... I had the same problem with my 1989 300CE with the M103 engine and it drove me NUTS for weeks- after throwing parts at it, I found that this was a COMMON culprit!

The OVP relay is located behind the black panel right in back of the battery in the engine compartment.

Lots of luck!

Mike

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