I had a mazda 6 in with very similar problems to yours, if i disconnected the Pre CAT 02 sensor then it would drive fine, this also had no fault codes logged.

This had a different sensor to normal (wideband i think its called) that works with switching a currnet and voltage feedback.

I attempted to scope the current output and signal voltage but as i don't have a micro amps clamp it wasn't that easy but did manage by looping the wire around my low amps clamp.

I came to the conclusion that the 02 sensor was lazy but at nearly £300 didn't want to take the risk so advised to take it to a dealer.

The outcome was a new 02 sensor and a MAF meter, i scoped the MAF as well whcih in my opinion worked very well.