1989 300SEL. Please tell me if this is normal. Checked duty cycle on X-11 with key on engine off. Reading was steady 14.9%. Obviously a California equipped car. Engine running duty cycle hovered around 49%. After reaching normal operating temperature, duty cycle reading started to steadily drop to around 35% with small up and down movement around 35%. The car idles around 550 RPM which is a little on the slow side. I believe specs call for 650 RPM idle speed. Should I adjust the duty cycle so it reads around 50% at operating temperature?

When the engine was revved up, the duty cycle kept going up with the RPM reaching about 85% at about 2000 RPM. Is this normal?

Also, the idle adjustment screw is still covered with the original aluminum tower with the steel ball sealing it. The Mercedes shop manual states something to the effect that on vehicles with electronic idle adjustment there is no need to mess with the screw. However, they describe a procedure to break away the aluminum tower and do some drilling, extraction, etc. that sounds a bit complicated. I also checked EHA current as described in one of Steve Brotherton’s posts on the subject. KOEO current was about 19.9x ma and slowly dropped to around 0.0x ma after starting the engine. I did some search on this subject and found a wealth of information that helped me carry out the two tests. However, I couldn’t find anything that specifically answers the two questions above.

Thanks

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Riadh
'89 560SL Rauchsilber
And what is good, Phaedrus, and what is not good -- Need we ask anyone to tell us these things?