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  #1  
Old 09-25-2007, 09:59 PM
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Join Date: Sep 2007
Posts: 13
'85 380sl idle speed problem

'85 380sl, 75K miles, generally extremely reliable and runs very well.

During last couple of months idle speed had occasionally gone to 15k then returned to normal 6-8k. Now stays at 15k +
Cleaned idle control valve with WD 40. Get function ( can hear click and see rotation of internal motor) on bench by applying 12v dc. When installed the idle speed is still at 15k. Only seem to get 6+/- v dc from plug powering the unit. ( Also tried second control valve from local junk yard - assumed probability of two bad ones low?) Idle speed does not come down with either control unit. If I power the unit with full 12v dc, engine stops.
Assume problem either valve or electronic control. Am I correct ? Anybody with similar problem and saved by something else ?
And where is that electronic speed control box hidden ?
Help !
Tullheinz
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  #2  
Old 09-25-2007, 10:14 PM
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Join Date: Sep 2007
Location: Phoenix, AZ
Posts: 4
Hi,

There is an Idle speed control unit behihd the glove box. It may be your problem.

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  #3  
Old 09-26-2007, 09:35 AM
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Join Date: Mar 2003
Location: Convent Station, NJ
Posts: 755
I also have an 85 380SL. I finally swapped out the Idle Control Unit with a known working piece and it solved my problem. Beware of Used Ebay units if not guaranteed. I was lucky enough to find a member here who had a working unit.

Below is a pic of it's location behind the glove box. Note that I had to pull the rubber vacuum tubes off the actuators (pink) in order to gain access.
Attached Thumbnails
'85 380sl idle speed problem-idle-control-valve.jpg  
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Rick

'85 380 SL (sold)
'85 Carrera Flatnose
'71 280 SL Signal Red/Cognac
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  #4  
Old 09-26-2007, 11:45 PM
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Join Date: Sep 2007
Posts: 13
Thanks very much. That was great and speedy help. Will pull the glove box liner and try a replacement control unit.
Sig
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  #5  
Old 09-28-2007, 11:01 AM
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Join Date: Sep 2007
Posts: 13
thanks again problem solved.

Many thanks. Especially useful was the picture of the circus behind the glove box. found matching idle control in local yunk yard, plugged it in and idle went back to normal. Also learned that WD40 does a good job removing some of the carbon in the idle control valve.
Sig
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