poor gas mileage

hi i have a 92 previ 4wd automatic with 198000 km the car is running strong and smooth,sparks,air filter,gas filter,pcv valve have been replaced but i am havong very poor fuel economy/ 20 liters will do 100km
any suggestions???
thank you.

Change your Spark-plug wires(To NGK) and also change plugs with NGK-irridium plugs. I did that and my American 8 cylinder car and gas mileage improved by 40% from 17mpg to 25mpg!