Kia Rio 1.6 2008 high fuel consumption

Good day all, i have a 2008 Kia Rio 1.6 Sport. The
car became very heavy on fuel a while back and we
had it diagnosed. It came back as an oxygen
sensor problem which we then replaced, the car
was also serviced at that time. The car kept being
heavy on fuel 5km/l or 20l/100km we have since
replaced the coils cleaned out all the sensors and
the manifold the car is still extremely heavy on
fuel. A new symptom also arrose with it idling fine
for about 10 seconds and then it starts misfiring to
the point where it completely shuts down. I have
tested the vvt solenoid, crankshaft position
sensor,camshaft position sensor, fuel pump and
injectors and all seem to be working fine. Please
help me figure this out, the car has been to three
technicians and two auto electricians with no
answer