2002 Pontiac Grand Am Fuel Milage

I just purchased this vehicle from a dealership "as is" after a customary look at it and a test drive. They assured a thorough inspection for safety and performace was completed. My first road trip with the car occured the next morning when I drove about 200 miles on a turnpike as well as about 10 or so miles of city driving. The gas milage for this combo was only about 14 mph. The car is rated at like 23 city and 34 highway. Despite this, the car starts excellent, runs smooth, accelerates what appears to be normally (it is a 2.2 liter 4-cyl), and makes no unusual motor sounds. My concern is with this crappy fuel milage.

I am planning on doing a traditional tune up (replacing the plugs, wires, air filter if needed, and probably coil packs) as a start. I have also looked around the engine for any vacume leaks. There is no water bubbles forming in the cooling system nor overt water in the exhaust pipe.

Do you know if there is some common problem with this engine that would cause poor fuel milage should the tune up fail (i.E. A sensor or something like that)?

I realize its a high milage vehicle, but I don't think thats the exclusive cause for the milage. Any direction I need to start towards would be appreciated.

~ Randy