I have a 1991 300E. It's been a great car. It has developed a problem, though.
The idle cutoff will not work. Until...you press the accelerator to the floor one time. No need to hold the accelerator down for any length of time; just a split second will do.
After you conduct the "Accelerator Maneuver", Idle Cutoff works perfectly.
The throttle position sensor and decel switch are functioning properly.
Pretty weird, huh?