wow that is low for that car. should be up in the 40's on the highway. Lot's of things to look at. Is it an automatic? If so do you have any slippage? State of tune is something, but what can really kill mileage is a clogged air filter. I use K&N High Flow in the original air box and get 2 mpg better. A clogged air filter is like choking the engine. Is your check engine light on, and you are possibly ignoring it? Could be a clogged or clogging catalyst.At that low of gas mileage for that car -- I would definately get a professional estimate of repairs needed. Do the things I could do myself, and pay for the rest. The repairs will pay for themselves at the price of gas nowdays.