Problems like this can be hard to diagnose unless u have a 2nd r33 u can swap parts with,
Things to try-
Disconnect the 02 sensor and go for a drive, any better?
If not
Swap afm with a know working afm and drive, any better?
Swap the ecu with a known working ecu and drive, better?
Swap the coolant temp sensor and drive( will be hot and may lose coolant BEWARE! )
Do a pressure test on the intake system
If above doesnt fix it, put it on a dyno and check air/fuel ratio's and the condition of the fuel pump.
Let us know how u go