our cars are designed to recirculate. what that means is that there should be a hose running from the bov to the intake pipe. the MAF takes into consideration the air that "leaks" from that bov and figures out the ratio of fuel to add to match that air. if the air is not present in the system, for example if you dont let the air from the bov BACK into the intake, the car adds fuel for air that isnt there, and therefore the idle is not very good, and/or acceleration is choppy.

in some cases, it doesnt have any effect on the cars performance. but more than likely, your rough idle could be caused by that, and the dying after revving it up almost solidifies the theory.