I'm having trouble diagnosing a high idle on my 1990 300SE and reaching the end of what I'm able to do myself.
Replaced all the vacuum lines and connectors, new plugs, wires, rotor, new fuel pump and filter, coolant flush, tried three idle control valves (no difference what so ever between them and tested to be working) changed both idle control valve hoses, new idle switch, new potentiometer, filter, oil, transmission flush and filter. Nothing I've done has the slightest improvement or change over the RPM, in P and N at around 1800RPM and in drive at 1000 RPM.
Ordered an overload protection relay and should be installed tomorrow .Car has 85K miles
Brought it to a local mechanic and he told me it could be the MAS Control Unit. Could this cause high idle and what does it do and can it be tested? Can't find anything about this module online?
