What pipes are under the metal inlet manifold?

[Adammcf]

What pipes are under the metal inlet manifold as there is a loud hissing coming from under it on my car all the time.
Ive had a look round it but cant see where its coming from.

[Guest]

its usually breather hoses, they can split with age. - can cause rough running if bad too.

[Adammcf]

Yeah I thought it was one of the vacuum pipes as the car is idleing a little rough at times. Its also using LOADS of petrol and its not just my heavy right foot either.
Looks like Im gonna have to take the manifold off and check each pipe to see which one it is.

[Brianmoooore]

Sure it's coming from right underneath and not the big rubber air pipe betwwen the air mass meter and throttle body?
What engine are we talking about?