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CEL Came on for O2 Sensor for 10 seconds, thoughts?

Posted by Earendil 
So I'm driving home late last night, making the 2000 foot elevation climb through twisty rmountain roads to get to my house, when the check engine light comes on and stays on.
I was not driving her softly, but it wasn't extreme either. At the point when the light came on, I was flooring it (or close) in 3rd gear at 2800 RPM. It was a steep hill with no rear ledge, so when the light came on I shifted to 4th to get the RPMs lower, and nursed it another 10 seconds to a place I could pull over. The light styaed on the entire time.
Turned the car off, back on, and a stomp test later got the fault code 1221, Oxygen sensor.
Restarted the car, drove it aggressively home (including a couple high RPM hits) and never saw the light flash again.

Any ideas what might cause a sudden, constant O2 hit like this? When I've dealt with this in the past, it's always been a short lived, and reproducible problem.
To have the light come on in 3rd gear at 2800rpm (flooring), and then to stay on while doing 2000rpm in 4th gear (half throttle) strikes me as odd.

This scenerio setting off any alarms in peoples heads?
Should I just ignore it?

Car was otherwise running fine, though there was fairly loud music playing at the time, and the windows were down.

1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

Edited 1 time(s). Last edit at 10/15/2009 01:14PM by Earendil.
Just a guess but I've had vacuum related times when I've had the CEL come on for a short time. One was a loose oil cap on the valve cover (only caught one tang), after I found the problem the light went off.

The odd thing was it stayed off for 15 miles and only came on after a good run through a few gears...

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