1990 chevy 1500 4.3 issues

[chevy3223]

ok i have a 90 chevy 1500 4.3 v6 and the nv3500 5 speed and i have problems when the engine is cold ill start it and it will start and shut back off and i can keep it running by hitting the throttle when it starts to die and it will stay running but when i try to pull out and drive it will sputter then come back and it will do that untill it starts to warm up once the motor is warm it will run just fine ive replace the idle air by pass, map sensor, pcv valve and it has the old style obd 1 computer so i did the paper clip trick and it gave me a code of 55 which means the computer is bad i replaced the computer and unhooked the battery then hooked it back up it is still doing the same thing and the service eninge light is still on and its still telling me the computer is bad but i dont believe that is the problem any help will be much apreciated thanks, Dan