Damn beats me.... I just know I'm having the same problem as the OP. I was told last time I had the car worked on it needed to be changed due to hole or flap... I figured it was something I could do myself and save the extra $$$The 02 ZX3 has the 2.0L ZETEC in it. Which PCV hose has to be changed is the question? There are several hoses involved in the system.