I'm sorry, I'm not clear. Right now you have the codes coming with using Chevron gas?
It could be the MAF still...car should smooth out if you unplug maf. I'd try that first and see what result you get.
If that smooths out the idle, I'd still say it could be a vacuum leak...0-ring/gasket issue...or if you haven't changed fuel filter in forever, that's another reason for lean codes.