couldn't help but notice the fuel pump relay wasn't mentioned - on my 300E (m103) when the fuel pump relay was toast, it affected the cars ability to start, idle, and often times made it stall (randomly). try replacing it w/ a known good unit (or trial and error with some $5 junkyard relays).

Its possible that water getting on the relay caused it to fail too - on these cars the gutter for the area above the relay can clog and then water seeps through onto the relays and causes all sorts of problems. I'd start w/ the FPR first.

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87 300E
202k on the clock