Subaru Impreza Engine Poor Mileage

After Purchasing The Car I Serviced It, Change The Fuel Filter, Spark Plugs Everything....but Still Having Bad Gas Mileage, After Careful...

Hi, I Imported My Subaru Impreza With An Ej15 Engine, (no Airflow Meter) Sometime Late Last Year From Japan. I Never Thought Of Calculating...