I drive a 2013 si coupe, which has been fairly beat on, by the previous owner and my self for the last 3 or more months. Recently, my mpg went from 25-26 to 17-18mpg. I’ve read that replacing the air filters (not done yet), replacing the spark plugs(not done yet), and running fuel injector cleaner (done but no results, stayed terrible). I’m checking my tires tommorrow and will be doing all these things in the next few days. Is there anything i am missing??