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Old 03-03-2004, 05:42 PM
Registered User
Join Date: Feb 2004
Posts: 19
560sl / Idle control valve or amp?

My '86 560sl occasionally idles at 1700rpm. The problem is intermitent & I've found that if I remove the wire from the idle control valve, and then put it back on, the car's idle returns to normal. Today the idle seemed to be OK until I would come to a stop. The idle would at first start out normal (10 seconds or so) & then bump up. I'm not certain if the idle increased when I pushed on the brake since I can't get the problem to repeat itself by design. Does this sound like a problem with the amp? Is the idle system a vacuum system and could a leak be the problem? The reason I don't think it is is that when I remove & replace the valve wire the idle goes back to normal. Thanks for any advice. Mike

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Old 03-06-2004, 12:34 AM
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Join Date: Jun 2003
Location: Chesapeake,VA
Posts: 189


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Old 03-06-2004, 08:21 AM
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Join Date: Mar 2003
Location: Indiana "the region"
Posts: 27
Here's my 2 cent worth. I would say You have diagnosed the problem perfectly. The ICV is sticking open and the act of unpluging and repluging jolts it bact to working. If the amp was bad you would not help to unplug and plug. Next time try just taping ICV to see if it starts working.

The KE control unit (fuel computer) has very little to do with warm idle. The idle is controlled this way. The throttle valve closed, air goes thru a hole in the fuel mixture assembly thru the ICV thru the air distrbution tubing straight to the fuel injector holders. The amount of air the ICV allows thru determines the amount of deflection of the air metering plate, thus the amount of gas to injectors. If the ICV stuck open to much air to much gas to much rmp.
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Old 03-07-2004, 06:05 PM
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Join Date: Feb 2004
Posts: 19
Benz Tek & Jeffmg, thanks for your reply. Jeff, I'm not sure how the valve works. When the valve gets power it closes, right? Therefore to open, increase rmp, it would need the opposite, less power. Since this problem is occuring when the car is warm and idle been normal for a long while why is the valve opening? ...and I wonder why it doesn't get stuck open under other conditions?
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Old 03-07-2004, 11:05 PM
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Join Date: Mar 2003
Location: Indiana "the region"
Posts: 27
Very good qusetions and I thought about that ater my reply. I don't know. I guess that it makes no sense the Idle valve would suddenly open and than stick open after being in the proper position.

You cannot ignor the fact that your high idle is caused by the idle valve being open otherwise unpluging and repluging would not affect idle.

The ICV is controlled by a circuit board called the idle speed control unit located under the carpet on the passenger side.
Anything is posible with a mercedes electronic circuit board!

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