Can you identify this pipe?

[BigSix]

Hi, I got some work done on my E34 535i, the mechanic closed a breather pipe on my fuel line with a piece of pipe and a screw. Im not sure if this was meant to be closed, Ive pulled an image off of the haynes manual to show you what im talking about.

Like i said at the moment it is blocked however I've unblocked it and felt a lot of suction coming from the pipe. It doesnt seem to affect the cars idle at all.

What is the correct thing to do here, block or unblock. My initial thoughts were that the pipe was a vacuum for something else. But the pic clearly show that nothing is connected to it.

???

Thanks

[BigSix]

somebody must know, this should be easy

[strad]

On my car it is capped off. Nothing is supposed to be attached there. You most definitely do not want any air coming into the engine from anywhere besides the AFM.

Oh, and edit: that is not a fuel line, it is vacuum supply for the vacuum booster.

[russiankid]

That is the check valve for the brake booster. I you pull that off, you should have a huge vacuum leak and the car should run like crap.

[BigSix]

Ah cool, thanks a lot. Much appreciated
Had to take out a faulty thermostat today. So my e34 getting a good look over. Now that I know thats a vacuum (they should label this stuff for me) Im gonna follow that line around the car and check for other leaks and so on, cause some days it just feels like there ain't any power.
I got plans to spend a lot of money on my car this week. Full custom header and free flow zaurst, service and anything else i got to do.