I see a million and one threads saying check for vaccum leaks, people saying they have checked and found them, etcetc, but no where saying HOW to do so. I would really appreciate this as I am still having massive acceleration, stutter, and a p0420 cat deficency light cel.

 

step one: start engine

step two: listen for hissing sound

step three: follow hissing sound to leak

 

What if engine noise over powers said hissing sound?

 

If your engine noise is THAT bad, you have more problems than a vacuum leak...

there are kits you can hook up with a pressure guage though that measures vacuum, if you have a leak it will show it...then just use the vacuum diagram under your hood and check all the lines

 

There are also 'smoke' checks that fill the system with smoke...

It is tough to 'hear' a vacuum leak - but with practice you can distinguish between the intake and the leak. Move your ear all around the bay - be mindful of hot bits and the fan! Think Safety! Touch/tug each vacuum line / run your hand down and listen. For manifold and TB leaks i use carb cleaner sprayed along possible leaks (gaskets) and listen for a change in the idle speed.

Still got a leak? Disconnect and plug vacuum lines at both ends (one by one) and see if idle stabilizes. The first symptom of vacuum leak is the idle 'surging' as the ECU is 'hunting' for correct idle compensation.

Lastly, replace each hose one by one (i have never gotten to this step - Thank God! )

 

Thanks guys.
The big problem is I have a nice CAI and it makes a good deal of sucking sound, so its really hard to distiguish betweeen that and vaccum noise. Plus, to be honest, I would not know the difference if it bit me on the ***.
I have been having off idle, hesitation, low gas milage, and stutter.... so I changed the spark plugs and wires. After awhile I got a p0420 cat below threshhold cel. I ordered two new o2 sensors, and plan to just do away with all my cats (Savannah has no emisions )
So the last thing I know of is the EGR valve and vaccum. I found my egr and plan to clean it up (little choke cleaner) but I have no clue about vaccum, so hense the post.

Thanks for the suggestions guys, I'll let you know if I burn off my ear.