Mercedes-Benz W201 idle control valve and unstable idle
Mercedes-Benz W201 what is the idle control valve (idle motor) and what does it do?
The idle control valve bypasses the throttle and lets air into the intake manifold for idling. The control unit adjusts how far it opens according to temperature: the more current the valve gets, the more it opens and the higher the revs. When cold, the idle is higher than when warm.
How do you test and clean the Mercedes-Benz W201 idle control valve?
Test: when you apply 12 V to the valve, it should open, and when the voltage is disconnected, close. Cleaning: remove the valve and hoses, and clean with electrical contact spray or brake cleaner, not with a lubricating agent. Do not scrape with a sharp-edged tool. A stuck valve can be freed by cleaning.
What other than the valve can upset the Mercedes-Benz W201 idle?
The air hose going to the valve may be cracked or have come off: the shorter hose cracks easily, and the pipe from the rubber tray to the valve can come loose. Such a leak can raise the revs to as much as about 2000. Replacing the hose or sealing the joint is often the fix, even if replacing the valve does not help.
Which way round is the idle control valve installed?
When the valve is in place, its shiny surface faces up.