If you truly wish to look, you should view the idle valve command with either or both an ammeter and a scope or duty-cycle gauge.
You didn't state a year so hard to give advise as to what to look for. Your statement that it went to 1800 means you probably have an 85 or older K-jet w/lambda. You are going have to get over the concept that the failure of a control module causes exactly "X" condition. Just ain't the way it works, lotta "grey" in this trade (as opposed to black or white).
The common reason for inability to control idle speed is an air leak. The module only can drive the early valves closed at 70% duty cycle. if its doing that either the valve won't close or air is coming from elsewhere.
Bosch Master, ASE Master, L1
33 years MB technician