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"Gretchen" my 1986 300E 286000 km+ (RIP) August 2015
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1,092 Posts
Discussion Starter #1
Today I went to check rich/lean setting at the X11, normally I'm right around 45-50% on the duty cycle. Now I'm getting reading way up in the 90%+. Car runs OK, but somewhat difficult to start
in the morning, then runs fine once its warmed up
I have recently changed the O2 sensor and didn't encounter any problems at that time only increased smoothness and a fine running car.(It was a bear to remove the original O2 sensor, but we got it out)
Any ideas on what I need to check to get back to original 45/50% reading? And what could have happened and what is happening?
 

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MB W124 300D 1986
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25 Posts
It could be a vacuum leak.

As I recall, the duty cycle increases with excess O2. The control valve will then put in less air, and the idle stays where it is suppose to.

It may however not be able to get rich enough for starting and cold idle.
 
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