02 Dodge Caravan (3.3V6) just started making a hissing sound 2 days ago when it's on. It a high-pitched sound, like air leaking out of something. It makes it whether the A/C is on or off. A/C still seems to work fine, so I'm not sure what it is. When I shut the van off, it continues to make the noise a couple of seconds after.

also, when I start it (even when it's warmed up), the RPM seem to jump up a little higher than normal, and take a few seconds longer to settle down. Any ideas? It's the long weekend, so I can't ask any co-workers. thanks for the help in advance
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I would say you have a vacuum leak. A vacuum leak will cause the rpm to be highter.

 

that's what I was thinking. It's not actually my van....but where should we look?

I haven't worked on a 3.3, ever (never really even looked at a 3.3)

 

Start by tracing back to what was removed or replaced.

 

My 03 had the same problem. Hunting I found a small hose (3 inches long) under the intake manifold that was cracked and leaking. Hard to see at first but if you take off the top of the air filter housing it makes it easier. Judging by le L-shape of the hose i figured it would be a dealer item, used generic vacuum hose and problem fixed.