I bought my 02 Yukon new and have never had any problems with it until recently when the service engine light came on about a week after I got gas at a local convience store. I took it to Auto Zone to run the codes and it kept showing "lean". So, the guy thought maybe I got some gas w/ water in it or something. So, he cleared the code and I went on my way. A couple of weeks later, it came back on. I went back and they ran it again. It showed the same codes, so I bought some octane booster and put high end gas in it. They guy that cleared the code this time said it might be a mass air flow problem. That was Sun. Today the light came on again. Any clues as to what it might be? I was thinking of letting this tank of gas run through and then clearing the code and filling up again and pray that's all it is. I doubt I can be that lucky. My MPG have avg. around 11 for awhile now. Is that a good gas mileage for this year and make? Thanks!