Opel corsa low idling and poor performance

Hi guys. I have a 2003 opel corsa 1.6is utility
bakkie, corsa B. I don't know what to do anymore.
When I start her up she idles ok but only when the
orange light on the dash comes on. When that
light is not on the Bakkie idles so low that it
sounds like it wants to cut out and when I
accelerate it sputter a bit before it revs smooth
and it sounds like it is running on 3 cylinders. At
this moment the Bakkie is so heavy on petrol that
I'm trying to drive her as little as possible. I have
replaced the crank sensor, the cam pulley, spark
plugs, plug leads, idle sensor, map sensor and the
tps and the Bakkie still does the same. Yesterday I
put in a bottle of injector cleaner and after a while
that I was driving I realize that my idling became
better but this morning when I started her up it
was back to square one. Can it be that I have dirty
or faulty fuel injectors? Please help, Im desperate
because this bakkie is my income. I need it to be
reliable for work purposes. At this moment I'm
getting only like 7km per litre petrol. That is damn
low for a 1600cc. Thanks in advance.