Tap on the ICU smartly and see if the RPM changes, if so the ICU probably has problems. That is what mine boiled down to. Either there are Cold solder joints or there is another problem. I kept my old ICU as a "get home" repair if the good one takes a dump and I'm stranded. Same with the old OPR.

Happiness is a MB that'll start and idle like it is supposed to.

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1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.