Ok ive got 02 altima 3.5 with code p0121 which leaves me stuck in failsafe mode:( ive replaced ecu, throttle body nd accelarator pedal camshaft nd crank senors all new 02 sensor nd still nothing ive with all through the factory service manual on here and cant find anything about this specific code iv tested almost all the wires for continuity does anybody know where i can find this code in the service manaul any help would be greatly appreciated

P0121 code is for a faulty throttle position sensor, did you check or replace it?

Yes ive replaced it and did voltage test on wire im getting the right low voltage a .77 but when i push the accelarator its spiking up to about 3.4 then drops right back to .77 im lost ive tried to do relearn but cant get it to do it im geussing because of that voltage drop