Hey! here is a little help......
You might have an other problem other then the ICV (Idle Control Valve) BUT
i can tell you one thing, this valve CAN NOT BE CLEANED!!!!!! many people try to clean it and that make's your car got nuts right after...
I will explain why. I did a couple try's with 3 ICV's from 3 different used cars, the rubbers seals inside will leak and break as soon as you shoot brake cleaner, intake cleaner or what ever else in there. I even tried to clean one with some Q tips to see if it would work and after every single time i touched one(cleaning wise) it stopped functioning properly. So ICV cleaning is not possible with W126's. ICV's it will not respond well and break (even tho current is still going through and looks like it's working it wont work well)
I bought 2 brand new one's one for my '87 420SEL and 1 for my '88 560SEL
for the 4th time i tried cleaning and "new one" even tho it didn't need cleaning, and BOOM guess what it was defective right after.... (i got it refunded and ask for an other one i know... i know...)

So do not Clean your ICV.... Actually this weekend i have a Costumer with a '90 560SEL with the same problem(high idle) coming to get his car fixed. If it's not his ICV it's a vacuum leak but, best bet is the ICV.

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1991 560SEL AMG "Jap spec"
1989 560SEL Euro spec