MIL code P1128

This code came on when I plugged in the scanner into my car, "P1128--Manufacturer Control Fuel Air Metering". Does anybody knows what this mean? Or how to fix it? My "CEL" has been on for the last 15,000 miles and I've been getting really bad gas mileage.

Thanks.

That would be a code for system too lean.
Check for vacuum leaks from vacuum lines.

If there are no vacuum leaks then either your maf sensor is bad or the front o2 sensor is bad. (maf covered 7yr 70k miles.)