Ox Sensor confusion

["Scott M." <scottmo@teleport.com>]

Regarding the use of a DMM to see how the O2 sensor
output voltage is responding:

 If your DMM has what is called an "analog"  bar graph you 
CAN view the changing O2 sensor voltage. These "bar graphs"
respond from 20 to 40 times per second and allow viewing
 more rapid voltage changes. As Graydon mentioned, at idle 
the O2 sensor oscillates around 1 to 2 times per second (1-2Hz) 
and at higher exhaust flows (higher engine revs) the response is
around 2-5 Hz. 

When I replaced the O2 sensor on my
 89 200TQ with 90K miles it had some of the slots in the tip
plugged up with carbon and this resulted in a slower response
time at idle which prevented the fuel system from accurately
keeping the mixture stable at idle. I also noticed a little surging
during the first 5 minutes of running after the O2 warmed up
and the system went into closed loop operation. After replacement
the idle mixture was now stable and the CO% was reduced out the tail
pipe.

HTH
Scott M.