All this talk about O2 sensors, and yes I replaced mine looking for 
the miracle cure to low fuel mileage and performance (how slowly we 
learn the inevitable).

Here's a nugget FWIW.  One can adjust the air mixture screw, in a rough but adequate sort 
of way, by hooking a *digital* voltmeter to the disconnected O2 
sensor lead and watching the changing values.  Adjust the air mixture 
screw to get as close to 500 mv on a warmed up engine.  A properly 
adjusted air mixture will give alternating high/low voltages on 
either side of about 500mv when the O2 wire is hooked into the 
computer and giving mixture feedback.

This is not a complete substitute for a 4-gas analysis (I'm still 
saving for the unit, buy it right after shoes for the kids) but it 
gets you close and is better than the random turning of the mixture 
screw we've all done.  BTW, if you do happen to have a CO meter, it 
is ESSENTIAL to take your reading at the test plug *before* the 
catalytic converter, otherwise you will get low CO values not 
representative of the exhaust.

Daniel Houg
Minnesota Department of Health
Internet Address:  fairwind@northernnet.com
Fax #:  218/755-3823