Low Fuel Milage/ Mileage/ How to Improve fuel mileage
There are a number of things you need to check. Do let us know how you calculate the fuel average.
1. Change the Petrol pump and see if that makes a difference.
2. Get your throttle body/Carburettor, MAP/MAF sensors cleaned with a good cleaner. Also get the IAC Valve cleaned, make sure to lubricate it with a few drops of ATF oil after cleaning.
3. Change your Air filter and see if a blockade has been installed if the car was or is being used on CNG. It can also be in the shape of tape which covers the air cleaner box letting less air going towards the intake manifold. If you find a blockade remove it!
4. Use STP "Complete Fuel System Cleaner" or any other good ones you can find. For better results use it more concentrated.
5. Change the fuel filter. Use genuine fuel and air filters.
6. Change your spark plugs, use stock plugs. Look for the recommended plugs.
7. If all this doesn't improve your fuel average, consider changing your driving style.
On being failed in all these, i changed the 'Fuel Pump' of my civic 2006 which is located inside the Fuel Tank