My O2 experience is the same as Robert's.
The thing was unplugged when I bought the car. The PO had a very experienced mechanic maintain the car; he obviously knew all the little tricks that make these cars run properly. The O2 sensor stays unplugged and the car still passes smog check easily. (Cat is still in place).
BTW, when I read my Bentley SC manual, I was astonished at all the components that make up the O2 sensor system. I suppose if you pull the wire on the sensor, all this stuff is just sitting there saying:"???????"
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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm