idle control valve
 

My 1991 190e 2.3 has a fast idle. It idles around 1400 rpm. I recently got the car running thanks to the help of this forum. It had a broken wire in the td signal wire from the control module( THANKS JOE BLOGG). All of the electric connections are correct as well as the vaccum lines and timing. What I need to know is when the idle valve is closed is it supposed to be completely closed or partially open? If there are any other suggestions as to where to look to correct the problem I'd appreciate the input. Another thing , I adjusted the idle mixture inadvertantly and think I corrected it pretty close, but would like to test it to be sure. How would I go about this? At a cold start it takes a bit to get it started and keep it running until it warms up a bit. Thanks for any help.

My oscillating (500-1200 RPM) and sometimes steady high idle (1200 RPM) where solved after I cleaned the idle control valve.
Mind you, I had to clean it 3 consecutive weekends before it was solved (one can of carburetor cleaner and one can of brake cleaner). Problem has not happen in over a month since cleaning it the last time (hence my assumption that it was the cause of the problem). Also make sure you lubricate it with WD-40 when done cleaning.
To adjust the mixture you will need a multimeter with duty cycle capabilities (US 30.00 in SEARS). Place the positive pin #3 of the diagnostic socket, the other in ground (or pin#2). Properly tuned it should oscillate around 50% at both idle and 2500 RPM. A deviation of 10% from idle to 2500 RPM is acceptable.
Example:
Oscillates 40-50% at idle
Oscillates 50-60% at 2500 RPM

This I learned from SteveBFL, credit him for this info.
Without people like him, Benzmac, and every single contributor of this forum, I and many others could not be able to afford a Mercedes Benz (at least the repairs).