might not be the same thing but.............. i had something similar sounding on my old xr2i years ago(its not turbo'd but still efi). wouldnt start normally and had to do the things u said to get it to run etc and after lots of ideas and lots of messing about i found out it was actually the connector that joined the fuel pump to the outlet in the tank (2i's had internal pumps not sure what urs is like?!) may be a long shot but it was literally just one of the rubber seals being perished that caused a loss of fuel pressure, the way i found out was if you take off the fuel return pipe on the rail and crank it if its getting enough fuel it'll pump loads out (obviously have something under where the fuel comes out to catch the fuel but if there is a fuel pressure issue u wont get alot coming out!! Also the other test was to spray carb cleaner down the throttle body as it'll pick up and try to run if its jus being starved of fuel.

Might not be anything to do with it but may help