Ryan,
I have a '93 300CE. There was reference to a idle switch for my car. We looked high and low for it. Finally we found it in the throttle linkage above the brake pedal inside the car on the drivers side. It was hidden in a black bracket. It is a simple microswitch that actuates when the pedal is depressed. We replaced it with no improvement for my problem. Good luck.
Anziani
'93 300CE 190K
'95E420 120K