Re: 1997 UK W210 e230 idle speed adjustment

Rather than adjusting to the fault the fault should be found and 
corrected. The motor is "hunting" for its ideal air / fuel ratio but 
failing.

I'd look for a small vacuum leak between the mass air meter and the 
intake manifold - a loose or cracked boot - or a cracked or disconnected 
vacuum hose. Such a leak of unmetered air introduces a variable that 
confuses the motor's control system.
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