I've not had mine off so can't comment on internals but as I understand it it is a control valve for the vnt actuator bolted to the turbo.
It's job is to control the vane angle in the vnt ring to either the stored map in the ecu or on the fly adjustments linked to boost map values.
Basically altering the turbo shaft speed to keep the boost pressure at a value the ecu wants.
The boost valve/vnt control valve is being fed maximum vacuum from vac pump or vac reservoir, the valve is then metering the vacuum fed to the turbo actuator( if i remember right when I tested my spare turbo the vanes started to move at -0.2bar and reached stop screw at -0.8 bar)
I'm assuming there's an electrical plug and solenoid similar to egr valve.
A variation in valve position should give variation in vacuum fed to turbo actuator.
There must also be some sort of vent to atmosphere to release vac when required as the actuator is sealed/ dead ended.
Most issues with vnt valve when I joined here were issues with the valve getting wet(especially with undertrays missing, possibly the vent filter getting wet and blinding up stoping release of vac maybe?)there was a fiat fix to relocate the valve up to the side of the battery tray.
Any splits in the pipe , if replacing them need to be vacuum pipe so won't collapse under vac.
Hope this helps and as I understand it, not saying this is correct.
That looks like the right part in picture but description is gobbledygook .
The price is too low to be an egr valve anyway.
Have you fond the noise to be the valve or just looking
Here's that link again
https://www.fiatforum.com/stilo/276358-boost-control-valve.html
It shows a valve split down to better understand it.
