T-dog sierra

Weird problem. The computer starts to drift after a while, I know that much. I was getting mass air and left back/right back running rich error codes. These codes combined with the rough cold start symptoms are indicators of fuel alcohol % wander in the ecm. You need to refuel with 10% ethanol or less in the entire fuel tank and then reset the fuel alcohol% with a scan tool. The ecm will then relearn the percentages and the vehicle magically fixes itself. I changed the mass air and it still threw the same mass air code. I reset the fuel alcohol and everything had been great since. I'm running a 2013 GMC sierra 4.8L V8 E85 flex fuel. I believe this is an issue for all newer(ish) E85 engines that don't have the old dedicated sensor. That New Dude description of the system was bang on. Read that and you'll understand why this fix works. Maybe yours is something similar and a 60 second scan tool reset might work for you?