Although the following info from "ALL DATA" is for a '95 E300D, Perhaps its applicable to you too

There is a Mercedes Technical Bulletin that describes the EXACT same symptoms that you describe. They attribute this to a faulty Over Voltage Protection Relay [OVP], specifically an internal Solder Joint Fault. A Computer fault code may or may not have been stored.

It seems that there was a batch of defective OVP relays. Also, did you by any chance change your OVP relay in the past for a used one?

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]