For me, mixed city+ hiway driving will get me 500-600km from full tank to empty. Very seldom to go below 500km even on city drive alone. This engine dont have VVT so dont drive too slow in expectation for lower consumption. 90-130km/h is fine (for me at least).

My last fuel fill up was last Sunday, just after my periodic servicing. And my fuel mileage is recorded at 609.9km (used Shell 95). I cant say ur engine is faulty or whatnot, just do a routine checkup, or replace anything that is overdue (plugs, filters, injector cleaning etc).

My car was 2001 made btw.