From my readings on the CPS awhile back, it seems that the CPS only has one job, identify when cylinder #1 is at top dead center. There is an article that someone else attached that I read that talked all about how the CPS works - if I still have that I'll attach it for you.

What I gathered awhile back is that if the CPS was totally bad your engine wouldn't fire, because it wouldn't know when top dead center was and therefore the CPS wouldn't tell the engine to send spark to cylinder #1 - so a completely bad CPS means no spark at all. But if one is on the fritz it could in theory cause rough idle and poor running of the engine because it knows when top dead center is only sometimes.

The other solution (that I would try first - in retrospect, as I still haven't done this yet, but did replace the CPS on my m103) is to inspect the ignition wires and coil as you have suggested. I have done a fair bit of reading on the coil and that can also exhibit similar symptoms if it is on its way out. In my case, it probably is the coil, the coil actually looks old in my car, which probably means it is old inside and not providing proper electricity to the distributor.

If you come up with something else, I'd love to know what it is, because I still have this problem occasionally in my m103, even though its only when the car is either wet or its raining out.

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87 300E
202k on the clock