will not idle after reaching operating temp
 

1992 190E 2.6. Car starts and runs fine, but after car warms up it doesn't idle. It will restart and stumble, but runs good with increasing RPMs. Help

Points to idle air control.

The air flow sensor position indicator (potentiometer) might have a worn spot at the idle position. Put a voltmeter between pins 1 and 2 (brown and blue/black wires). With key on, engine off, press down slowly on the air flow plate and make sure the voltage goes smoothly with no sudden jumps up or down. If you have an autoranging meter it is best to disable that feature to prevent confusion when it changes ranges. I had the same symptoms on the '89 260E.

Also make sure that all the HT components are in top condition and are MB original or, second best, Bosch/Beru. NOTHING else. Cheap, copper, non-resistor plugs too.

RayH

I have the same issue on my 85 280ce. I'm running NGK plugs but I have a set of Bosch plugs as spares. I was told NGK is the best plug to run for this engine. What should I check on mine? The injection system was rebuilt along with the warm up regulator so I'm pretty sure it doesn't have anything to do with that.

Non-resistor whatever make. NGK works fine in mine, as do Bosch originals and Beru. Never tried Champion but they are listed my MB for my car.

RayH