http://www.kitesolar.com/car_fuel_mod.htm This mod restores the fuel efficiency by as much as 20% improvement over factory.
What are needed are a set of tin snips and some material suitable for a restrictive plate. I used some copper sheet I had laying around.
The Mass Air Flow sensor mod tricks the O2 sensor as air flow around the MAF element is lessened. The computer recognizes less air so it squirts less fuel. The O2 sensed at the catalytic convertor will achieve a stable level when the flow of air is restricted somewhat... To do this the computer modifies the fuel mixture.
I might see more improvement without sacrificing performance by covering the maf sensor slightly in my 2007 Spectra5.
I think it may do better than the 5 miles per gallon improvement I am seeing in my KIA Spectra5 but it is a sports sedan. Your car may do better or worse. Also don't mess up the MAF sensor because they are supposed to be quite fragile.