I have been asking myself, after waiting a minute of course, how does the engine know it running one way or the other at cruise?

RPM signal says the engine is running X fast. A load input say from the speedometer? Maybe, but on these cars? Doubtful!

AMM air flow is an input but not after the fact it's just sending it's perimeter issue signal. Or at least it's suppose too!

So rich or lean is after burning? Ok, it's reporting, I am getting to much or not enough.

The ECU says "I see this much going in and I adjust this. You, the O2 sensor, are telling me what?"

"Hold the phone here, I gotta go turn on a light, the emissions are off!"

The ECU is now saying, "The sole purpose of the idiot light, is "emissions" related. My job is done, I will notify the "Idiots" outside my black box. I am really done here! It's "Out of Range" of my capabilities!"

My conclusion, within my "self imposed" imaginary conversation, is the ECU or is not, getting correct information! If it is, one or the other, is going "Wonkers." Or was, that a chocolate factory???

If it were really bad, the car would run that way! Is it or is it not? That's a question, Mr. Watson!
He is the other, great big computer on the "information" block, but you can answer that one! (:-)

IMHO the AMM is a fairly stable instrument but that O2 guy is working in a hellish environment.
Especially if things go wrong long enough!

I would put in a new Bosch one of those and make darn sure that any and all connections to the ECU are great. Measured every end point connection, every which way, from the last Yesterday! (:-)

Or as Jack Nicholson the actor said, "Is this, as good as it gets?"
By listening to that, make sure the AMM connections are clean and top notched as well!

I think the answer lies in what their doing and how the ECU interprets "What's going on out there?"

I know, you are asking the same thing!
My answer, is not much better than yours either!

Just my way of thinking and writing about the problem!
(:-)

Phil