Why does my mazda etude 1.8 sedan 1995 have high fuel consumption on 1995 Mazda Protege

My mazda etude 1.8 litre sedan 1995 model is very heavy on petrol. It does about 430km on a 50litre tank and I do not know how to fix this problem. I bought it recently and it has had the same consumption since. It has 244000km on the clock. I serviced it recently, changing the spark plugs, oil and air filters but it is still doing 430km on a full tank. The timing belt makes a slight squealing sound and the car sometimes jerks a bit during acceleration when I am driving on the highway. Could this be what is causing the high fuel consumption? What could be causing the jerking and what should I do to get a fuel consumption rate of at least 12km on a litre.

Asked by for the 1995 Mazda Protege
Check between mass air flow sensor and throttle body for any leaks or cracks in intake hoses. Check accessory belt(s) for proper tensioning.
2 more answers
These BP-engined Etudes had poor fuel consumption upon release, but it can be repaired.
I drove one for 7 years averaging between 11 and 12km/litre.
Timing needs to be adjusted to around 11 degrees BTDC and mixture leaned out - you will need proper equipment to be able to do this(agents). The exhaust system is very restrictive; I fitted 50mm s/s piping(3 x 57mm boxes).
Problem solved. A less restrictive air filter will also help.
i exactly have the same problem pliz how did you solve this i have the same car and 1996 one