What is this thing ?

[X5-D-Sport]

E53 D sport 2005 UK Right Hand Drive...

On the inner wing in-front of the washer bottle, there is a large sausage shaped thing, with ribs on it....

NO it is not a sex toy before we start.

It has a 10mm od / 4mm id tube out of one end.
When the tube is pulled off the nipple, the engine note changes to a deeper tick-over sound at the exhaust & back to normal when plugged back on, even tho the revs remain the same.

What is this device & what does it do ?

Any ideas ?

[X5Sport]

Vacuum reservoir for the turbocharger control. If you leave it disconnected you’ll have a distinct lack of boost. Connected and it excites the performance of your engine ...

[X5-D-Sport]

many thanks... defo leave it connected.

[Alan Gunn]

When i first got my e53 that was the first vacuum pipe to fail (day after i got it ).