+1 to the AAC valve and the AFM clean. Regarding the random stalling, my pervious R33 sometimes would do that when I stopped at lights etc. Cleaning the AAC value fixed that. I would also suggest resetting your ECU after you clean both the AAC valve and AFM. You can do that by disconnecting your battery and pressing the brake pedal a few times.
In regards to the adjusting the idle speed, I believe the best way to set it is to connect via a consult cable and use some software (free or paid) to lock the car into what is called "base idle mode" when the car is hot then adjust the screw on the AAC valve. I think you can lock the car into this mode without a consult cable however I can’t remember how to do it. This way you can set the idle correctly as the AAC valve (as well as other systems) are taken out of the loop. This is what I do when I set my idle on the GTST and GTR. Using this method I find my idle speed to be perfect.