I have an 04 Yukon XL. About a month ago, check engine light came on. Took to my mechanic. Said it was a lean fuel code and to put some additive into gas tank. I did this and it seemed to work. This weekend, it got very cold where I live and engine started to idle rough. RPM's and engine would surge while in park or at a stop light. Took to mechanic today. Computer said MAF sensor was bad. Had it replaced along with fuel filter. Seemed to run normal again while at the shop. Once I got it home, I put it into park and the engine started to surge again while in idle. Although it was not as profound as before, it was still surging. Any suggestions on what to look for next? Thanks for your help and have a blessed week.