check ovp, spark plugs and wire connections, check voltage regulator and test alternator for stalling issues. As for the high idle, check the iacv, also try turning the small wheel being the gas pedal counter clockwise (I think) you might have to follow the pedal up a bit by the upper portion of the foot well, or you can take off the air cleaner housing and adjust the knob on the throttle cable to reduce idle

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1990 190E 3.0L