I've been having occasional rough/low idle problems much akin to vacuum leaks (rpm will keep going up and down from 100 to 500 rpm, chugging the engine) and have noticed an intermittent hissing noise (psshhhh - pshhhhh - pshhhhh) coming from the PCV hose going to the intake. If I pinch the PCV line, the hissing noise stops. Is it normal to be hearing this from the PCV/PCV hose, or is it likely there's a leak in one of my vacuum hoses somewhere? Most of the time the car runs just fine, it's just one day out of a week it'll suddenly start chugging and dying on me, then work fine the next day. I'm going to guess that it's a leak somewhere in a hose, but I'd rather hear what you guys have to say before I take the manifold apart to check the PCV connection.