P0446 Toyota -

Question

would this cause the RPM needle to go up and down and sometimes make the engine die?

Answer 1

P0446 Evaporative emission vent control malfunction

Sure it possible, if it  is the purge vacuum line at the throttle body is disconnected,What making the RPM unstable is false air or vauum leak , this can be from a torm MAF (mass air flow ) air duct from MAF to throttle body, The unstable idle can be from a stuck open EGR valve, , What you have is a vacuum leak As for P0446 this is mainly the vent control at the charcoal canister located near the fuel tank Check for ruptured emission hoses that tends to crack at their connection