Greetings fellow Pwx's

On a couple of occasion's over the last week my car has stalled at Traffic lights/ Stop & Give way sign's..
And when driving at normal road speed's the car has stalled when driving and fired again ( IE rpm's go from 2500 to 1800 and have nothing no power then back up to normal rpm) and have power and thottle usage back.. when it stalls I turn ignition off and back on and it starts up
Car has just had minor service a week ago and a major service 10,000 k's ago

Done some searching and am thinking, air fuel module, o2 sensor, knock sensor.. But am not 100% sure
Car is a a 2005 Wrx Impreza Wagon
No mods that I know off
other than CBE
not sure if it has a tune

any help would be helpful or if any one else has had this problem
Cheer's Josh