well first of all you have a 13.2 gallon tank and your car should get 24-30 mpg considering it over 100k take 2mpg off that so your getting probally 22-28 take 1 mpg cause it a auto thats 21-27 your tank scale is 8-10 gallons I forget say 10 so 10 times 23.5 is 235 miles a scale tank 104 times 2 is 210 so your probally getting about 21 miles a gallon change your air filter and spark plugs that should help get a CAI that will also help