[Signman]

If open loop the O2 Sensor is out of the equation but stills is reading way lean if the plugs are showing very rich.

If the MAP sensor is the problem why not just unplug it. The ECU should go to a predetermined value and should adjust the fueling with TPS and Temp Sensors. Probably very similar to Alpha N.

Go into the fueling map while running and lean out the cells being used paying attention to the idle rpm and how the car sounds.

Lower the fuel pressure will lean out the whole map.

Just throwing out ideas.

If the sensors you are using are all used unknowns get everything new, Rock Auto is about as cheap as you may find unless your local parts supplier gives you a good discount.

If you are not confident in working with the fuel map call your tuner or bring the car back to him. May be money well spent.