I have a 2014 GT sport and ever since I got the car it’s had terrible mpg (like 7.1mpg). I don’t drive like a lunatic and no matter how I drive my mpg stays around 7- 9. What in the world can this be?
Also try cleaning MAF, throttle body, and cleaning or replacing engine air filter. As other suggested, clean fuel injectors and have spark plugs checked. My ‘11 GT S MC gets about 17mpg combined (13 city, 20 hwy). I am lightly spirited driver. Just to double check, you are putting 93 octane at least in the tank?