Clean your MAF. Fords have an issue with the MAF getting dirty and causing a lean condition. It can even get so lean to throw a code.
The best way to clean it is using spray contact cleaner from radio shack. You want point it at the wire. Do no touch the wire, only spray contact cleaner on it. The problem being, that the wire gets coated with dirt/oil and airflow accross it does not register properly.
Do you have a K&N? Often, the oil will come off the filter and collect on the MAF. Even oil accumulated on the wire could throw a code, because it insulates the wire and prevents it from giving a proper flow reading.