I would like to mention that proper preventive maintainence plays an important role in fuel economy.
I have a Honda Civic EXI 2003 1500cc manual, it is very fuel efficient provided you maintain it well, it is 170k driven with routine preventive maintainence from Honda 3S is giving 13-13.5 km/l in city, my city drive consists of 70-80 km/h about 50% of journey and daily drive of 40-50 kms and highway mileage tried on recent trip to Multan with four adults and luggage on board and it gave me 17.33 @95-100km/h with light foot.
I was trying to remind that which one maintainence job improved my cars performance considerably?
About an year ago my Civic was not giving smooth ride on petrol and heavy fuel consumption i.e. 10km/l beside all preventive maintainence by Honda 3S and this thing was biting my mind.
So one day I took it to the workshop and asked the foreman for test drive and when he was driving I asked him that there might be a possibility that its fuel filter is choked as my car had already done 155k, he said we need to check.
So I got it checked and it was really choked upto the neck and as a result all the debris were being deposited in throttle body causing heavy fuel consumption and rough ride.
So I got it replaced with new OEM fuel filter costing Rs. 5800 and when we inspected the throttle body it was having too many carbon deposits although it was serviced just 10000 kms before and as per the manual it should be serviced after 20000 kms, so I got it serviced too and the result was mind blowing super smooth drive and awesome fuel efficeincy of 13.47 km/l as I mentioned earlier as well.
Maintainence always pay, I have Toyota Landcruiser, 1989 model, HJ60 3980cc, non-turbo, 6 cyl diesel, 5 speed manual, you wont believe its mileage, it gives me 8-8.5 km/l in city and 10 km/l on highway at a speed of 90 km/h as this machione is not meant for high speed driving due to bad aerodynamics but again I spend too much on its routine maintainence but its worth.