poor gas mileage 390 km to a tank 2005 cavalier PLEASE HELP
 

hi there i have a 05 cavalier with 70,000 kms on it and at most i will get 400km to a tank even with highway driving almost the same amount of kms city or highway. what can i do to improve that i have put in more expensive gas and i will get maybe 5-15 kms more. do i have to replace anything what do i have to do .. thanks for your help