"Geoff" wrote in message igy.com...
snip

I found what I was looking for if anyone is still interested -
http://www.autoshop101.com/forms/h64.pdf, the top of page 4 shows the plots
of HC, CO, and NOx efficiencies versus air-fuel ratio.

That is the same document I posted above. Thanks for the more direct
link. Here then is the direct link to the Toyota document for oxygen
sensors.

http://www.autoshop101.com/forms/h37.pdf

The first line is:

"The ECM uses an oxygen sensor to ensure the air/ratio is correct for
the catalytic converter."

I hope the "evidence" is good enough.