About a month ago my Burban started running real crappy. At first, I thought I got a tank full of water. The truck would start, immediately go to Fast Idle then it would backfire through the throttle body as well as out the exhaust. I can work the throttle to keep it running, but it pops through the exhaust and through the TB and I am constantly pumping the throttle to maintain some state of the engine running. Well, every once in a while it clears up and goes back to very Fast idle. I finally ran the tank down real low and drove it sputtering all the way to the gas station. I filled it with Premium and about 3 cans of Heet. It still sputtered on the way home, barely pulling itself at times. I sat in the driveway doing my normal pumping of the throttle while it backfired as before and finally it went to "Very Fast Idle" again (probably somewhere around 3000 RPM) and it stayed this way for about a week. Every time I drive it, even when it warms up, it stays at the 3000 RPM idle. Well here I am just below a half tank of gas again and was driving down the interstate and the darned thing went into its popping fit again. I thought I had it cured of that since it drove for a week at fast idle but no popping. I've checked the codes with engine shut off but key in run position. All it does is flash a 12 code over and over. No other codes in this mode. When I start the truck, with the code reader installed, the Check Engine light blinks at a slow rate and does not flash any codes, it just blinks steady. Sometimes when I rev it up in this mode, it blinks faster. So, anyone had this problem? Grim, how was your Burban running when you had that problem, and what was the problem/fix? Thanks for the info. I know this is vague, but its the best description I can give.