This may sound rediculous, but it has worked for me. If you have abnormal readings from the oxygen sensor & can't find the reason, try changing the engine oil. For whatever the reason, changing what appears to be clean oil can make a difference. I put in the thinnest oil available at the time, run the machine for a day, then change again & put in the correct viscosity. I've had this happen a few times with newer trucks with O2 sensors. It's the first thing I do now with driveability issues.