Sounds like you are having some of the similar problems that I had. I have a 91 300E. Check out my thread "Owner of a 91 300E looking for a cliff"

I replaced several things all of which temporarily helped but i now suspect they just needed to be replaced as maintenance.
I replaced...

• Spark Plugs
• Spark Plug Wires
• Distributor Cap
• Fuel Filter
• Fuel Pumps

Finally the Pumps are what did the trick, Turns out the primary was overheating then killing. once the car cooled for bit it would start right back up only to do it again.
*I replaced the fuel filter twice, Once a couple hundred miles before a, once during the pump replacement.

Hope it helps.

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It's the little things that hold the big picture straight.


1991 300E - Present Car
1988 300CE - Gone but not by choice.