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1985 380SL
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48 Posts
Discussion Starter #1
I know this can be a common occurrence with these things, but I wasn't able to find a thread on it to save my life. After working on some things this last weekend getting it ready to finally take possession, I noticed it to intermittently idle really high. Sometimes it starts up cold and idle at 800-900 just fine and other times it will start up and idle at 1,500. Then sometimes it can switch to the opposite of whatever it's at (i.e. 800 up to 1,500 or 1,500 down to 800) after it's been running for 15 minutes or more and up to temp.

So I know there is the Idle/Air Control Valve as well as the Idle Control Unit. Is there a way to tell which might be causing my problems based on my symptoms? Any way to test either of them? Thanks guys and sorry if I overlooked a previous thread on this.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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I know this can be a common occurrence with these things, but I wasn't able to find a thread on it to save my life. After working on some things this last weekend getting it ready to finally take possession, I noticed it to intermittently idle really high. Sometimes it starts up cold and idle at 800-900 just fine and other times it will start up and idle at 1,500. Then sometimes it can switch to the opposite of whatever it's at (i.e. 800 up to 1,500 or 1,500 down to 800) after it's been running for 15 minutes or more and up to temp.

So I know there is the Idle/Air Control Valve as well as the Idle Control Unit. Is there a way to tell which might be causing my problems based on my symptoms? Any way to test either of them? Thanks guys and sorry if I overlooked a previous thread on this.
Any other symptoms, ie hard start, (don't guess it has ABS or light might also be on)...
My OVP was intermittent in manifestation of its failure...
 

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1985 380SL
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48 Posts
Discussion Starter #3
Any other symptoms, ie hard start, (don't guess it has ABS or light might also be on)...
My OVP was intermittent in manifestation of its failure...
I barely touch the key and she fires right up every time. The ABS light comes on after about 10 minutes of driving, which is a whole other story. (Until the light DOES come on the antilock system kicks in near the end of each stop. Like I'm driving on ice and starting to skid. Really annoying.)
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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7,150 Posts
I barely touch the key and she fires right up every time. The ABS light comes on after about 10 minutes of driving, which is a whole other story. (Until the light DOES come on the antilock system kicks in near the end of each stop. Like I'm driving on ice and starting to skid. Really annoying.)
Idle problems when abs light is on?
I strongly suspect OVP (could not remember if car age of yours had abs)
 

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Previous: 1989 190E 2.6, 1997 E420, 1985 380SL, 1975 450SLC
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747 Posts
Next time your car's idle is high, pop the hood and wiggle the fat green wire leading to your car's EZL module (located on inner fender behind the left headlight cluster). If that fixes the idle, search here for 'green wire' for the fix. This worked for my 85 380SL which had the same symptoms as yours.
 

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1979 450SL Anthracite with red interior, 17" AMG wheels
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509 Posts
nathanso, interesting, I'm certainly going to try that too, thanks for the tip. sometimes it's these little tricks that are worth the most.

Try this link, and go to 'busted motors' then to 'high idle hell'
northernresource.com/mercedes/107-repairs.htm
 

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1985 380SL
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48 Posts
Discussion Starter #7
nathanso, I searched and the only thing I found on the green wire fix was the thread you started which gave me somewhat of an idea. It sounds like I just need to inspect the prongs on the ICU end of the green wire and pry them back to normal if bent?

Thanks for the link Gohot that's a nice short-and-sweet article right there.
 

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1985 380SL
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48 Posts
Discussion Starter #8
Okay so I had my grandpa check it out since I'm back home and the green wire is a female end on the ICU side so I'm really confused now. Can someone provide a link to this "green wire fix" thread that I can't find anywhere?
 

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Previous: 1989 190E 2.6, 1997 E420, 1985 380SL, 1975 450SLC
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747 Posts
Okay so I had my grandpa check it out since I'm back home and the green wire is a female end on the ICU side so I'm really confused now. Can someone provide a link to this "green wire fix" thread that I can't find anywhere?
The green wire's plug on the EZL side is actually coaxial, i.e shielded from what I could tell. It was the three contact leaves in the outer part of its plug that had flattened out over time and were making an intermittent connection. Wiggling the green wire near the EZL during a bout of high idle should temporarily lower the idle to around 700 indicating that your plug's three contact leaves need to be bent outward to make a tighter connection to the EZL's jack. If wire wiggling doesn't cure your high idle then I'd look elsewhere. Oh, a concurrent symptom of my car's problem was the tachometer reading too high (2X actual) and unsteady during the first five minutes of driving after startup.
 

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1985 380SL
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Discussion Starter #10
The green wire's plug on the EZL side is actually coaxial, i.e shielded from what I could tell. It was the three contact leaves in the outer part of its plug that had flattened out over time and were making an intermittent connection. Wiggling the green wire near the EZL during a bout of high idle should temporarily lower the idle to around 700 indicating that your plug's three contact leaves need to be bent outward to make a tighter connection to the EZL's jack. If wire wiggling doesn't cure your high idle then I'd look elsewhere. Oh, a concurrent symptom of my car's problem was the tachometer reading too high (2X actual) and unsteady during the first five minutes of driving after startup.
Interesting. I don't think the tach is reading wrong and it doesn't run rough during the first few minutes after startup so maybe it's not the problem but it's worth a check. Thanks!
 

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Previous: 1989 190E 2.6, 1997 E420, 1985 380SL, 1975 450SLC
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Interesting. I don't think the tach is reading wrong and it doesn't run rough during the first few minutes after startup so maybe it's not the problem but it's worth a check. Thanks!
The tach needle was unsteady; not the engine.
 

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1983 380SEL
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470 Posts
Sort of unrelated - but I had an idle computer go bad in my 83 380sel years ago. I replaced it with one on ebay and it drove like a dream.
 

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1985 380SL
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48 Posts
Discussion Starter #13
Was at the grandparents today so while I had a chance I removed the case from the idle speed controller and messed with while running just like the instructions said in that "High Idle Hell" writeup and sure enough she kicked down to about 800rpm when I would get the sweet spot. I took a soldering iron the main connections just to heat them up and hopefully reconnect whatever was missing after several attempts I couldn't get it to help any. Main thing is that I pinpointed the part that was giving me the trouble so I guess I just have to cough up the money for a new one. Thanks for all the help on this guys!
 

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Previous: 1989 190E 2.6, 1997 E420, 1985 380SL, 1975 450SLC
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747 Posts
Was at the grandparents today so while I had a chance I removed the case from the idle speed controller and messed with while running just like the instructions said in that "High Idle Hell" writeup and sure enough she kicked down to about 800rpm when I would get the sweet spot. I took a soldering iron the main connections just to heat them up and hopefully reconnect whatever was missing after several attempts I couldn't get it to help any. Main thing is that I pinpointed the part that was giving me the trouble so I guess I just have to cough up the money for a new one. Thanks for all the help on this guys!
Glad you found it. Be sure to clean out your ICV and verify the wires leading to its plug are sound as one theory goes that the ICU gets stressed trying to control a recalcitrant (i.e. sticky) ICV. It would be a shame to toast your new ICU.
 

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1985 380SL
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48 Posts
Discussion Starter #15
Glad you found it. Be sure to clean out your ICV and verify the wires leading to its plug are sound as one theory goes that the ICU gets stressed trying to control a recalcitrant (i.e. sticky) ICV. It would be a shame to toast your new ICU.
Copy that nathanso. I'm still at the grandparents so I think I might give it a soaking right now.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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No reason to leave until the left overs run out.:D
 
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