Engine shutting off when trying to accelerate from a complete stop or just shutting off while idling

Recently my car has been having some problems such as shutting off when trying to accelerate from a complete stop or just shutting off while idling. An example of this is when I was driving to school yesterday morning it was driving fine before and after I got gas but then I came up to a stop sign and when I went to accelerate the car shut off and I had to push it off the road. Other times before this I would go to accelerate and it would drop below one thousand RPMs when at a complete stop and shake a whole bunch and then finally go. So far I have replaced both the bank one O2 sensor and the idle air control valve and its still doing the same thing. I am just wondering what else it could be because I don't want to be spending tons of money on a part that is not causing the problem. Thank you for your time and help.