I have been trying to fix a surging idle and what I thought was a rich idle mixture on my 380SL (the Wayward Woman), believing that either my lambda controller or the frequency valve was at fault because of the duty cycle reading I was getting and because I could not hear or feel the valve vibrate.

It turns out that a new oxygen sensor stabilized the idle. AND, following the Steve B - Cap'n dialog, I was able to determine by measuring the sensor's voltage that the idle mix is actually a bit on the lean side - .27 volts from the sensor. So (I think) the frequency valve is going to be silent since it is staying closed trying to richen the mix.

Why exactly I am getting a lean reading now, when it failed it's emissions test earlier is unclear, but I suspect that I fixed a vacuum leak as part of the head and timing chain replacement that has been done since the test was done.

Details are on the Vintage Forum.

Anyway, thanks to Steve and Cap'n for the great diagnostic information. Hope Cap'n gets his problem solved as well.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

That is the real purpose of this forum, where we can learn from others with similar situations!! Glad it helped you and I appreciate your wish for help on my problem, I need it!!