just read the top again.... my car used to do this intermittently. Never found exactly what it was but i know since i put the microtech in and got rid of the afm as well it hasn't done it.
If it's a quick stutter then i'd say coilpacks.
If it's a big cut of power that sends ya forward in ya seat when it happens then it might be afm (this is what mine used to do)
Things like this are annoying coz it's hard to find the fault without looking at several things..
good luck