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  #1  
Old 08-03-2017, 03:43 PM
Jorn's Avatar
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MAS Control Unit cause of high idle?

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?



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Black on Black 1979 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE
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  #2  
Old 08-03-2017, 04:56 PM
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Based on the schematic from the FSM, it doesn't look like it:

http://i.imgur.com/g9RFq1A.png

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  #3  
Old 08-03-2017, 09:04 PM
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Thanks, very helpfull. It was loose in the socket and I secured it again, didn't change anything.
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Old 08-03-2017, 11:29 PM
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Jorn - you've likely seen this thread:

89 300E, W124, M103 High idle... SOLVED

There's a bit of sobering truth by Frank Reiner in post #7
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Old 08-03-2017, 11:40 PM
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Quote:
Originally Posted by Mike Murrell View Post
Jorn - you've likely seen this thread:

89 300E, W124, M103 High idle... SOLVED

There's a bit of sobering truth by Frank Reiner in post #7
I did, I've spent nights reading up on it. I think I'm getting close, today I got the idle down to almost normal by adjusting the Air Flow Meter-Potentiometer, only for it to go up again when I restarted the engine...

See my other post: Air Flow Meter-Potentiometer OEM vs Ebay

Quote:
Originally Posted by Mike Murrell View Post

There's a bit of sobering truth by Frank Reiner in post #7
After reading that, I decided it was maybe time for professional help...

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