I have Daihatsu Mira ES 2014. I bought it in 2018 and it was giving excellent average of around 17-19km/l.
I have driven it for 2 years and the average has been great( minimum 15.5km/l).
For the last 2 months, car is giving the average of maximum 12km/l and minimum 8km/l. I don't know what is the reason.
I have changed the engine oil( using helix 5w30), oil filter and air filter too.
I have reset the odometer 2 to 3 times. Whenever I set, it gives average around 22km/l on a smooth 70km/h drive and then drops gradually to about 11 or 10km/l.. The area in which I have been driving for last two months is congested and I drive at average speed of 20-40km/h.
Kindly suggest some effective measure. 
