gas millage improvement

I'd like to improve the gas millage on a 2002 Lincoln towncar
I heard that there ase modification kits available for certain cars that improve gas millage
It is something to do with the computer settings (the car loses pick up but the gas milage is improves by 4 miles a gallon in some cases)

Does anybody know if there is something like this available for the towncar and is so where to buy it?

Thanks

the only thing i can think of is setting you car to run lean but i wouldn't suggest doing that because you can hurt your engine. free flowing intake and exhaust can help but you'll most likely spend more on the exhaust than you'd save in gass mileage. the best way to improve gass mileage is to drive conservatively, don't accelerate fast from the stop, don't speed on freeways (wind resistance increases exponentially with speed so if you double your speed, you quadrouple the wind resistance) and this should save you gas, any mods you get will probably cost more money than save it in gas.