I have been trying to tune out a little idle hunting and fast idle that was
left over after replacing my AFM. I have done that by adjusting the idle
setting and CO mixture, and have been watching the O2 output with my DVM.

I seem to be getting strange readings from my O2 sensor. On some occasions,
it seems to read fine with a warm idling engine in closed loop -- I can
clearly see the readings oscillate back and forth crossing 0.5 volts.

But other times it just seems to stay at about 0.6 volts and does not
waiver at all, except to increase momentarily when I increase the throttle.
Again, this is warm, closed loop operation. If I disconnect the sensor from
the cable harness and just read its open loop output, it reads 0.2 volts.
If I close down the AFM CO screw I can only get it up to 0.4 volts.

Is this the sign of a dying O2 sensor? This one only has 12,000 miles on
it. I thought they just slowly degrade, but this one seems to be ok
sometimes but not others.

Or is there something else going on here?

John