For a service manual, Mercedes recently posted them all online free for use, here is a link to the 124 manual:
https://www.startekinfo.com/StarTek/outside/12264/?requestedDocId=12264
https://www.startekinfo.com/StarTek/outside/12264/Program/matrix.htm
As for the high idle issue:
My 190E would do this from time to time. I actually think its somewhat normal for the car to high idle (~1000rpms) on a cold-start. Once I get the car in gear and driving the idle returns to a normal 700-800 rpms.
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