CA18ET SPLUTTERING AND LACKING POWER...??

my ca18et bluebird is fucking me around. randomly splutters and lacks power under load but once boost kicks in its fine, if u nana it its fine. have done new plugs, leads, crank angle sensor, diizzy cap and rotor, fuel filter. tried different coils, two different ECUs, air flow meter off s12(exactly the same). adjusted valve clearances, checked and adjusted timing, set throttle valve switch. no sign of any vacuum leaks.
I havn't tried replacing fuel pump yet(because they're not cheap new and hard to come by 2nd hand) but i would have thought if fuel pump was fucked it just would stop working not randomly piss around.
it does give me trouble code 31 which means ECM but thats pretty vague.
also not sure if its related but vacuum/boost guage needle flutters, not sure what this could mean?
I'm running out of ideas and patience with it.
If any one has had any problems like this or has any ideas please let me know
cheers

any exhaust smoke?

not really maybe a tiny bit sometimes, it always leaves lots of carbon on the back door.