Thanks for the help on this. Here's an update.

I replaced the sensor with a single-wire Bosch. After the engine warmed up it appeared to get into closed-loop and had just a slight rythmic surge. The sensor output was fluctuating around .5v. When I drove the car, it felt a little perkier.

So today I am going to see if I can get a duty cycle reading and tweak the mixture if necessary.

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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