You'll mostly notice a decrease in gas mileage and you might even be burning oil. PVC stands for positive crankcase ventilation. The pcv valve is located on the intake manifold. It's purpose is basically to regulate fumes from the crankcase to the intake manifold where they can be burned otherise the fumes would blow seals and stuff in the crankcase and then the fumes would just go into the atmosphere. That's a purpose of the pvc system. I can't really explain more about but thats all I know. But don't neglect the pcv system as it can cause huge problems in the long run. I think it also prevents a little blow-by and sludge. It's a pretty critical system.