There are about 4 different types of idle control valves on MB engines, they all use different controls. The last versions starting with the M103 engine pulse voltage signals, ie: duty cycle. The 1984 to 1986 190E have a 3 wire set-up on the idle valve.
Most common failure is aging of the solenoid windings.
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)