I had the exact same problem on my car. Unfortunately, replacing the O2 sensors was the fix for me. These are the post-Cat sensors that we are talking about.
Could the cats be fouled up therefore leading to consistently high oxygen levels? I highly doubt this, but I'm not sure how much of an impact these things could have on the O2 sensor readings as you've seemed to eliminate most of the other culprits.
I would check the MAF a little more closely with a voltmeter.
Could the cats be fouled up therefore leading to consistently high oxygen levels? I highly doubt this, but I'm not sure how much of an impact these things could have on the O2 sensor readings as you've seemed to eliminate most of the other culprits.
I would check the MAF a little more closely with a voltmeter.