Got a 2000 V70XC AWD SE w/167k miles. Fixing it up to help a friend.

Got a inconsistent engine flutter sound at 2500 RPM under load. Put a VIDA/DiCE tool on it and boost pressure development seems inconsistent. Suspecting the CBV valve and checked it. No flutter sound on decel that seems to be common when CBV fails. Here are the stats

- Holds vacuum perfectly so silicon diaphragm is good
- CBV starts to open at around 4.5-5 PSI. This seems very low. I read LPT CBV's 8lb spring are not suppose to open until 8.75 PSI

Was wondering if anyone else know what PSI when the CBV starts to open? If anyone wants to do a quick 5min test, just hook up a Mityvac's vacuum to the CBV hose right at the manifold (green line connection to manifold in the following pic, its not the exact same engine but pretty close and CBV hose is exact same location). Set vacuum at say 8-20 PSI at 1 PSI intervals. If you hear a "closing door noise" near the turbo, its the CBV closing (which means it opened).

Note any tuned or HPT turbos likely have higher PSI when the CBV opens due to stiffer spring so stock LPT turbo CBV data is what I'm looking to compare to. Thanks