Odd CEL behavior ??

[Chris'91'525i]

My CEL started to come on intermittently right before my battery died. Replaced the battery and light stayed off for approx. a month. Fueled up car one day and it has been intermittent on-off since then.

Like yesterday had an appointment in Napa (wine county) ,round trip 44 miles. CEL was on nearly the whole time there, on the return trip it was off, ten came back on just before I got home and came to a stop.

Car history;Car is at 160K miles. O2 sensor replaced at 55K. Car failed, then just barely passed CA emission test after a new Cat was installed at the last test. Car runs great with no indications of anything wrong ! ( except the CEL)

I did a 'stomp' test and the O2 sensor is the only thing indicated. Stomp test did not operate as it should though, it would continue to flash the O2 code over and over without stopping. Left it for 15 minutes and it was still flashing O2 code without doing it's end code thing, so I could clear the codes by holding the petal to the floor for 10 Secs.
Any ideas ??

I'm going to check the wiring to the O2 sensor this weekend, but I don't have a sensitive enough voltmeter to check the O2 function. If the wiring looks good and cleanly connected I'll probably pull the O2 sensor and try burning the carbon off it with a torch. If no change R&R O2 sensor.
What has me baffled is how the CEL stomp test does not operate as it should.
Open to all ideas.

TIA