I have been troubleshooting a bad idle, no idle high idle, and an abrupt, though intermittent dying problem at idle. On slow down for a turn or a stoplight or sign.
I changed the OPR and it fixed it for about twenty minutes.

I noticed that when I would tap on the ICU when it was idling(high or low) that it would change (up or down) or die completely. ICU was suspect, but I could not rule out other things.
I bought a recently rebuilt ICU on Ebay. I installed it this morning.

VOILA! that seems to have worked. now starts and idles(first at about 1100, but drops back to about 900 (in park) almost instantly.) It now idles at about 600-700 in drive or reverse. Drove about 25 miles and it worked perfectly in all modes!
WHEW!
I really need it to idle right when I take it in to have the Smog test done. I feel really good about the car now, as I had the oil changed and they checked the spark plugs and all were firing right(they're new). All looked just like a good firing spark plug should look. Oil filter was TOAST! Can you spell falling apart! Car had had Castrol in it all it's life so I put that back in it (20-50) Am thinking about Synthetic after i get the little oil leaks (none underneath) fixed.

Now to get the CCU fixed. I tried to re-solder connections but I think it was toast before I started(some traces burnt through, Nothing working but one motor(heater blower on low??? and crosstalking I'm sure)so I have to get another. Blower motor OK as it worked intermittently, either with AC or Heat. I also bought a good Heater/AC relay
Before I put in the new ICU I took the old CCU out so as not to take a chance on a faulty CCU doing damage to the OPR or the ICU.

One by one I'm getting through the small problems on this fine old car. I am a happy camper today!

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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.