Volvo Repair: fuel consuming, electronic control unit, fly wheel

Question
hi deaR REGIS ,
  I don't know if you still remember me but I have a 940GLT  model 1991" with ( B234F ) 16-valve engine I used to ask you a questions about the the fuel consuming and I am still suffering from this problem , I changed the injectors (280 150 749) and the Air mass meter (280 212 016) and the throttle position switch and the I changed the tempreture sensor and in my car I don't have oxygen sensor in origional but I have the plugs for it under the right thrust near the fire wall so I made a hall in the exhaust and fixed one there and connect it and I made a compression test for the cylenders and the results was all around 11,9 and also I checked for vacum leak and for fuel leak and I cleaned the throutle body and the mainfold and I checked the connectors for the injection and ignition computers and checked the distributer and the plugs wire and the timing balance and the coil and the power stage , and after all that the car still idling alittle bit raugh and the rpm is moving between 900 and 750 rpm and the CO outlet is 6,7% which is too high and when I rise the engine to around 4000rpm the co goes down to under 0,5% so what I have to check else ? could the knock sensor or the position sensor on the fly wheel cause that ?
and do I have to doubt the ECU ( Electronic Control Unit ) ? what I have to do after all that ? just sell the car , I am gonna be crazzy of it so please help me  

Answer
I never did like the 16 valve motor seemed like alot more moving parts,oil leaks and more money to maintain with no benefits whatsoever.

never rule out the ECU.it may be interpreting a signal wrong and thus causing a problem with the injection timing at idle.

I would check fuel pressure I have seen some pressure regulators go bad casing high fuel pressure which will spray more fuel causing high fuel consumption.