Very similar to problems I am having with my 89 190e. Turns out I had no voltage going to the idle air control valve. Still trying to track down where the voltage is lost but have unplugged to ICV and it has not done it since. Might want to try that until you can figure out if you have voltage to the ICV or not.

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89 190E
2.6L
Arctic white
Grey leather
Sunroof
Pirelli P400 rubber
Smoked corners