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[mickb]

Hi everyone Ive spotted an issue with a hose under my bonnet it seems to have collapsed in on itself as if it was under suction Ill try to describe where it is as I havent figured how to put up pictures yet one end is fixed to a silver round thing just above the heat shield for my exhaust headers and the other end is fixed to a black round thing which sits on a bracket coming off the powersteering fluid bottle ? can anyone tell me what this hose does ?

[Abiton]

Sounds like part of the Secondary Air Injection system.
During cold start an air pump under the nearside front corner of the car sends air into the exhaust manifold to create an 'afterburner' effect which helps heat up lambda sensor and (mainly) catalytic converter more rapidly than it would otherwise, so reducing hydrocarbon emissions which can be considerable at this operating phase.

There are two valves in the system, a non-return valve to stop exhaust fumes coming out towards the rubber pipework (the metal round bit you mention), and a flap valve at the other end of your dodgy hose which is controlled by manifold vacuum mediated by a solenoid valve.  This latter valve is oriented and controlled so that air cannot pass into the exhaust except during the minute or so of SAI operation at coldstart, as this would otherwise confuse the lambda sensor and stuff up your mixture control. 

Not sure why your hose appears to have collapsed, maybe just degradation of the rubber through heatsoak?

[MutantCav]

I could be wrong but from memory I think this happens if the valve fails...I'm sure if I'm wrong someone will correct me

[mickb]

Thanks for the explanation guys  it fits in with some other problems im having, on start up the car is fine but as it gets to running temp it starts running poorly as if its running out of feul, this could be the answer. is there any way to test the solenoid before I replace the hose ? thanks again guys 

[Abiton]

Sounds to me like the poor running at operating temperature might be quite unrelated to this pipe.
I could be wrong though.
Take the rubber hose off the flap-valve pipe stub (black plastic) and look up the hole to make sure the flap isn't melted/missing or jammed open.  And take the other end of that hose off to see if it is very sooty inside, which would indicate that the metal non-return valve is leaky.

Look up 'Paperclip Test' in the Maintenance Guides Index and see if you have any fault codes in your engine ECU.