SLIGHT POPPING NOISE??

Ok, while in lower rpms and driving I sometimes here a slight poping noise. It sounds like a valve popping open or shut. My car also starts to jerk around while I am just cruising in 4th or 5th at like 2000rpms as if I were at extremely low rpms. The cables are all correct on the cap, which is msd. Sometimes the car rides rough and sometimes it doesnt. I also have a vacuum leak that I can seem to find....

If anyone has any suggestions it would be greatly appreciated, thanks

found out what it was...had two vacuum leaks. Once I plugged them up car ran perfectly

Well I have a trickflow intake and they were tucked up under the right side of the intake. I had two, one was pointing towards the front of the car and one towards the back.