The IAC shouldn't cause intermittent stalling while off idle.
I'd suspect an intermittent electrical sensor or connection. Unfortunately, this is likely to drive you crazy unless you get lucky early on. If it failed completely, it would be much easier to troubleshoot.
My priority would be the ignition system. I'd first check to see if any DTCs were stored in the PCM. If so, use them as the basis for your diagnostics. I would also look at any freeze frame data, if available.
In the ignition system, I'd check the coil electrical connector first, then try a crank sensor.
It might also be a fuel delivery problem. A fuel pressure guage would tell you is the pressure is dropping and causing the stalling.
Good luck, you're likely going to need it.
Steve
