What's This Hose For ?

[Patrick-Irish]

Take a look at the picture on the first link :

Vacuum control

See the Vacuum Pipe (part #6), and where it attaches to the rubber boot on the left. There's a recepticle nipple there for the hose, but just under that there is a much smaller nipple, almost small as a needle. See this link for a closer view :

Hot-film air mass meter BMW X5 E53, X5 4.4i (M62)

What is that smaller one for ? There is a tiny little hose coming off that and it laces it's way back to the rear of the engine somewhere. But I cannot find that little hose on any diagrams or part searches. Mine has actually broken off completely at the recepticle and I need to replace it but I have no idea what the hose is called, what it's for, where it goes or what it's part number is.

Any ideas ? This is all part of an investigation I'm undertaking into a faint but noticable hesitation pattern in the engine while driving.

Thanks !