1990 300SE Suddenly rough idle, rough runnin'!
 

So the old girl ran great last night but when I jumped in her this morning the idle sounded awful. It almost sounds like a cylinder miss. Under moderate acceleration the engine sounds very rough as well. Its a very blurb-blurb-blurb sound. Its strange though because the problem is slightly intermittent. Between 2400 rpm and 3000 rpm the engine sounds fairly normal again. On top of that there were a few times when the blurbiness vanished for a few moments.

Are there any electrical components I can inspect that might fix this? I should mention that my serpentine belt let out a nasty squeal this afternoon and looks a little worn. Is that related to my issue?

Check for loose spark plug wires?

Checked that first. Will check again though....

ignition check /replace
 

check distributor for tracking on inner side or rotor for high resistance /burned tip . Ignition wire connectors for grounding .

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Exactly, and don't economise on distributor parts, MB original is worth it in the long run although I've heard that Beru is good. I have Beru wires and all seems well.

Also, nice cheap copper plugs from NGK or Beru are the best - no resistors or exotic multi-pronged devices.

RayH