Well, disconnecting the O2 sensor seems to have done the trick. All that, and al I had to do was unplug the O2 sensor connection under the hood! . Anyone replace their 02 sensor with a single wire one w/o the heater?

Looking back it's interesting to see how misleading my initial symptoms were - "cutting out in corners" It was much easier to diagnose on the street - good thing I live where there are lots of unpatrolled back roads!

wow . good news you found the problem ... now what ? newe sensor and it's all good ?

Hmm all that effort for a simple O2 sensor. We need to put that one farther up on the troubleshooting list.

You can run without an O2 sensor completely. I did so for while, but I got sort of a lopeing idle with that. So it idled better with the sensor so I left it in.