[D.Johns]

I've seen where a two-step would intermittently come off and on during a run as the car vibrations made the switch connections. Picked it up on the data logger for the ECU.

Also seen where the O2 sensor has went bad threw the computer into safe mode since when the sensor fails it fails lean.

Check TPS and throttle opening 100% physically.

Could be a valve hanging open at the top of the rev range or ring flutter also.

Lots of possibilities just have to start the process of elimination with any data you have.