It counts A LOT, the same car, the same city, the same petrol tuning etc. etc. I got two different averages only because of two different routes (12.5 - 13.5 km/l on a relatively longer but empty road and around 8 km/l on a road with stop and go traffic and a lot of brakes to apply, even the course was significantly shorter). The car i am talking about is 1300 cc automatic BTW.
point is , if you drive on a busy road with a lot of traffic (jam) and stop and go ... this is already okay average, but it will improve after the tuning and oil change InshaAllah.