What is this? *with pictures*

InfernoFiero wrote: What does this pipe do?

It leads to Narnia.  Yes.  Most definitely.

Of course, there's also a slim chance that's it's the hinge for the air door, and not really a tube.  We are looking at the side of a duke air cleaner, right?

Oh..  were you talking about the small tube facing you, or the larger one pointing down?  That hooks to the exhaust shield (via the flex pipe), and just provides warm air on startup.  Around here it's warm enough it really doesn't do much anyhow. You could remove it and never notice the difference.

Loud idle...  chance are the exhaust manifold is cracked.  They almost all did it.
This lets air in, giving a false lean signal. so the ECM pumps in more fuel.
Then you get the carbon and sooting, and a 'rich mis-fire'.

Yeah, that aluminum tube (dryer duct!) that goes down to the manifold/exhaust, it would normally go up to the tube sticking out of your air cleaner in the first picture.

When it's cold out, the door in the tube/air cleaner housing opens up allowing preheated air into the throttle body. As the air heats up, the door closes and lets fresh cold air from the outside in.  It's the same thing they've used on carburated engines since the 60's (earlier?).

Anyhow - not that important.  Find that exhaust leak.  20X more important.  If you can't find another manifold, pull that one off and Damien or myself can weld it up probably.