Ya know my AE92 4A-F does the same thing with the new carb setup now.. I don't know why.. I'm also having radiator fan problems.. I've checked all the wiring and it's all good and the relay is also fine but the fan won't come on when the engine hits the right temp.. It was working fine before I ever started this project.. I was told by someone that the stuttering may be caused by the thermostat being bad..
I knwo what you mean though.. like you stomp it and it stutters like it's going to stall and then VROOM it goes.. weirdest damn thing..