[chuckm]

Do you happen to know if your vehicle has a MAP sensor? I can't be sure without the diagram, but I'd think the MAF, the O2, and MAP sensors all work together to determine the amount of fuel injected. Often, if one sensor is faulty, then the PCM will throw out the faulty reading and rely on the other two. In your case, the O2 reading should have been coming in high, leading to additional fuel injected. However, the PCM may have assumed your O2 was faulty and relied upon the other two. If that was the case, you may well have been running lean.