I have a 2005 Kia Amanti. I love everything about the car except the gas mileage. The government web site says it gets 15mpg in the city. I seem to only get 11. I have changed air filter and checked tire pressure. The only thing I notice odd is when I take my foot off of the pedal the car tends to not deaccelerate very fast (it likes to stay at 40 for example). I'm thinking I have a vacuum leak that is causing the computer to have a heavy idle. Any thoughts.