Like the title says, my computer is throwing the PO171 code. AutoZone's diagnostic says the probably causes could be something with the MAF, defective oxygen sensor, ignition misfire repair, or fuel injection problem. How do I know which one? Btw, I only got about 27 mpg this tank. The CEL came on today and I just had the spark plugs and drive belts replaced yesterday but this shouldn't have anything to do with it....Any help?