EDS/ELR Idle Issues - OM603

[Diseasel300]

This is an '86 300SDL OM603

I've been chasing an intermittent idle "miss" for some time now. The car will intermittently and randomly "shake" at idle, especially when in gear. Very similar to the behavior you get with a miss or "skip", although I haven't been able to track down where.

Imagine my total shock when I disconnect the ELR plug on the solenoid on the IP and the engine suddenly runs SMOOTH. AS. GLASS. In complete and utter disbelief, I jumped in the cab and raised the RPM up to 650ish where the ELR usually maintains and the car continued running completely smooth. No shake whatsoever!

So what on earth would be causing the ELR/EDS to make the idle shaky? I assume it is hunting? A related issue is occasional idle RPM stuck ~1000 RPM, then slowly dropping back to normal. I've caught it in the act and unplugged the ELR solenoid with the idle speed instantly dropping. Plug back in, and right back up to ~1000 RPM.

EDS computer going flaky? More bad caps/solder joints? Crankshaft position sensor? Am I just going crazy?