The car used to get EPA mileage (21/31/25) but now it gets 22 in the summer and as low as 15 in the winter, depending on the outside temperature. These figures are for mixed driving. The car has had this problem for over two years.
I have taken it to a dealer and a garage and neither can find the problem because it's not producing any diagnostic code or a light on the dash. I have had the air filter and the spark plugs changed but neither has affected the mileage.
My car has 55000 miles.
My car has an automatic transmission.
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