My engine stops all the time!

I've a 2001 grand cherokee and it often shutters and turns off. No noise
when it does it, just the car shakes and then cuts off. It happens only when
i drive it about 2 miles or more, and then sit idle at a red light. Once it turns
off, the Preform service flag comes up on the thing on the ceiling. But it
turns right back on without issue. Occasionally it sputters while driving, like
when there is air in the fuel line, but there isnt, that happens less often than
the engine problem, (which is nearly every day.)
Last week the check engine light came on. I've CLEANED and then
REPLACED the idle air control valve, we also replaced the throttle. Every
mechanic i have taken it to says they need for it to turn off and have the
engine light come on to pull codes for their computer, otherwise it reads as
nothing wrong with it. but, its not like i can guess when it cuts off. some
days it doesnt do it at all... I dont know whats going on please help