1988 Toyota 4Runner dosent get enough fuel

88 4runner 4wd v6 truck runs but wont rev over 1200 rpm im a technician and cant solve the prob ive changed fuel pump strainer and the filter the pressure is good its not the regulator or the tps or the cat or the mass air or the injector wiring or the body and engine grounds ive checked these items but if i hold the throttle down and pour a little gas down a vac line it revs up so its not the dist could it be the computer witch i doubt because if i disconnect the mass air it cuts off like it should. if i hold the throttle down it just surges and backfires
i dont know what else to do please help