Why would my car hesitate and jump periodically

Like it is about to stall for a few seconds and then not stall? It seems to be happening more often. Maybe, now 2-3 times within 2 hours driving time. I initially stopped using the air-conditioner and that seemed to help at first. But, it is still happening now. Also, the check engine light has been coming on and off since I got the car three years ago. I have been told THIS is probably caused by a loose gas valve.