I own a 2005 Toyota Sienna and right now I am getting about 12.3 mpg as read by my onboard computer . Most of my driving is in the city. I should be getting around 17 mpg for city.as advertised. I have changed my oil and all of my air filters. My car only has 70k miles. The engine is very quiet so I dont think there is a problem with spark plugs. Can you give me any ideas on how to improve my mpg. I do not have a lead foot just to add so my acceleration is gentle.