I have a 92 300E that is driving me crazy. It has a really high idle. I have read post after post with no success. I can't find a vacumn leak. I have changed the OVP 3 times. I have changed the idle air control valve three times. All the valves I have cleaned extensively. I changed out the MAS twice. OK, When I changed the valve, I cranked the car and the idle immediately went to 1800 rpm. I unplugged the idle valve and the idle came down to 1000 rpm. So I plugged the valve back up and the idle remained at 1000. I shut the engine off and then started it again and the idle immediately went back to 1800-2000. I then unplugged the water temperature sensor, both fans came on at that time so I figured it was ok. I also checked out the throttle linkage and found nothing unusual. Anybody have some suggestions? HELP!!!!!!!

Alright, I just went and changed out idle air control valve with a different one I had not used before. Also, I changed out short hose on intake side of valve & rechecked vacumn connections under intake manifold again. Engine had cooled down already. I cranked car and idle went to 1000 and stayed there until water temp gauge started climbing. As temp gauge climbed to normal so did the idle climb to 1600-1800. Cut car off, restarted engine and the idle climbed right back to 1600-1800. It was at 1000 until the temp went up. Could this mean water temp sensor is bad?

After some more research, could carbon build up on throttle plate cause the idle to rise? The idle signal is not getting through or the wrong signal IS getting through. Could the MAS be receiving or sending the wrong signal?

Possible unmetered air a air leak after the air mass sensor.

It can't be that difficult. Clean your air sensor plate and see what happens. Probably nothing. Have you ever changed your O2 Sensor? That causes idle issues if bad. OVP is a myth solve...sorry you replaced 3.

Try replacing you air mass temperature sensor, this is what I did to fix my m102 on my 190E.

PN W0133-1626014

Thanks for all the help. I checked everything you suggested. Still had the high idle. I had two items left to investigate so I picked the hardest one of the two(normally it is always that one). I had to fabricate a short headed 90 degree philips screw driver to take it off and replace it. It was the throttle position micro switch. I changed it out with a moderate amount of aggravation and the car idles perfectly. Thanks again. I hope someone else can use this information.

Good catch! I never had that issue but remember reading about others that did. That little plastic wheel gets brittle and chips away.