Easy way to detect a bad ICU is to rap it with a screwdriver handle while idling. If the car dies OR the idle changes with the rap, then the ICU is bad. That is how I found a bad ICU on my 380SE.

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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.