"Gary" wrote

Jim,
You have it backwards. EFI uses pre-programmed settings until the
engine reaches operating temperature. Then the system enters "closed
loop mode" and uses output from the O2 sensor to provide "fuel trim"
data which offsets the preprogrammed values for minimum emissions.
Some later model cars have electrically heated O2 sensors to allow for
closed loop mode quicker (EPA lower emission requirements).

Do you know of any web pages that discuss this type of thing? I would like
to read more.
--
Jim in NC