Idle speed
 

How do you test Idle speed control unit and idle speed control valve on 1985 380 SL Mercedes. I do not have any special tool as far as electronics.
My car 1/20 times when its hot(normal) does idle just fine, and other times idling too high around 1300 to 1500 rpm. When idling high, if I disconnect the Idle speed control unit and reconnect it back then most of the times Idles fine and other times idles up and down and keeps going up and down.