I have a 83 500sl thats idling at about 1500-1600rpm. I'm using the testing from the Service manual CD. Disconnecting or reconnecting the connector onto the idle control valve causes no change in idle speed. With a multimeter I'm reading approx. 13 volts from the connector that plugs into the idle control valve. If I push the connector part of the way on the idle control valve and try to get a reading by connecting the multimeter to the still exposed portion of the idle control valve I get nothing. If this is the correct way to test this the manual says I should be reading 5v +/- 1. Am I understanding the testing procedure in where I am trying to read the 5v? If I apply battery voltage to the idle control valve the idle drops to approx. 500rpm. If this is correct, then it appears I have a defective idle control unit. I have previously removed this unit from the car to look for broken solder joints, didn' find any but, resoldered around the connectors as I read this was a common weakness. Are there any parts forward of the idle control unit that could cause the idle control unit to appear defective? Any thoughts or suggestions would be appreciated. Marc

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1983' SL500 euro

I have replaced hundreds of the control units.

That said, you should also check the idle switch.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Benzmac,

When you say "idle switch", would that be what the manual refers to as the "throttle valve switch"? And if so, would you mind telling me its location? I'm having trouble determining where it is from the pictures on the CD.

Thanks for your help.

Marc

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1983' SL500 euro

I've done some digging. The CD service manual has the 380sl and the 560sl. This car is a euro 500sl.

I looked at the removal/reinstallation section of of the throttle assembly of an 86' 560sl.

I see in the picture the switch would be on the right side of the throttle assembly when facing the car, directly opposite of where the throttle linkage connects.

There is no switch on this car. I see the two holes where I believe the screws that would hold the switch on would go and it looks as though there is a plate/plug in between.

I read on one of the testing procedures "Vehicles with throttle vavle switch". This would lead me to believe that some models did not come equipped with the throttle valve switch.

If this is the case, and this car never had the throttle switch, would you agree from my previous testing that my problem is the idle control unit?

I appreciate your help.

Marc

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1983' SL500 euro