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Old 10-13-2003, 02:27 PM
sms sms is offline
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Join Date: Dec 2001
Location: Hartford
Posts: 134
560sl rough idle

I know there has been a lot of discussion on rough idle problems, but from reading prior posts I haven't seen anyone list the most common problems associated with rough idle on a 560sl. I know that some of the ideas are vacuum leaks, overload relay,fuel distributor, injectors, 02 sensor, ezl, air pump, etc.

My car has ~ $79k miles and I've replaced the wires, plugs, cap & rotor, fuel filter, and have used the techron cleaner, but no change.

The car starts and accelerates well. Even cold idle is ok. It's just once the car is warm and idling the rpm hunts in about an 60-80 rpm range. You can hear it hunting easy. I've checked for vacuum leaks using the carb cleaner method, but have found no leaks. The exhaust is a bit stinky so it might be o2 sensor, but don't know how to confirm? Also, I know there are a lot of electronic checks to perform on lambda and other controls, but only have a mutimeter.

Any ideas on how to proceed would be very welcome.

PS. Also have checked and cleaned idle control valve and egr.


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Old 10-13-2003, 03:11 PM
it leaks, its german
Join Date: Mar 2002
Location: raleigh nc
Posts: 1,111
Checked the base duty cycle. (CO) On the l/f inner fender is a black, roucnd connector, take off the cap, put the positive probe of your DVOM in pin#3, ground the other, set the meter to duty %, warm it up and set it in the 50% range. (3mm allem in the middle of the air cleaner, between the intake opening and the fuel head) Sounds to me like its just a tad lean hot and a small duty tweak will clean it right up.

Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
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Old 10-21-2003, 11:58 PM
sms sms is offline
Registered User
Join Date: Dec 2001
Location: Hartford
Posts: 134
Joe P,

Measured the lambda between pin 3 and ground and it read between 54% - 66%. Is this normal and if it is what else could be causing the rough idle?


PS. Along with the rough idle I also notice that the exhaust is a bit stinky.
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