Q: My Aura XR has code PO442 and the purge valve is pulsating on 2007 Saturn Aura

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The check engine light was on so I went to Autozone to get the code. PO442 says I have a vacuum leak. I looked at the lines and didn't see anything wrong but notice the Purge valve located up by the engine was opening and shuting. Sort of a pulsating sound. My suspicion is that it is bad but I wanted an opinion. How do I know it is not the evaporator vent valve causing the pulsing? I checked the cap and cleaned it up so it shouldn't be leaking.
(1) Answer
If the valve is operating, I wouldn't assume it's defective. You need to diagnose this "small leak." This is one of the trickiest types of evaporative problem to diagnose or find. "Small leaks" are often gasket or hose problems, or could be defective solenoid valves if the pintle doesn't seat properly. The gascap could be defective even if the seal is clean. There's a calibrated vent in the cap which could fail.