How do I set my idle in my 190E? It's not like anything I've ever worked on before.

The idle speed is controlled by the ECU through
the idle stabilization valve and is not adjustable. If the engine is not idling properly there is a malfunction in the system, which could be something as simple as high resistance at an electical connector, or a misbehaveing throttle position switch that is not telling the ECU that the throttle is at the idle position.

Lots of discussion of idle speed problems in the archives, which should give you a good education. Being as how the system is fairly complicated, it's helps to have good system knowledge of the various components that affect idle speed control.

Duke