Header problems
 

I am totally lost. I purchased a pacesetter header, and removed my stock manifold. Upon doing so I noticed that there is a piece inside my left exhaust port loose, and can be removed from the engine, but the piece in the right port is still firmly mounted. I have no idea what this piece is but it appears to me that this should not have happened? Well upon putting the header on, now the car does not want to run, it is like it is sufficating??? I also noticed the stock manifold gasket has a hole near the lower left mounting bolt, but the header does not have a hole for this. Do I have the wrong model of header maybe or is it not running due to the piece being loose???

The loose piece of metal you are referring sounds like the exhaust sleeve in the rotor housing. I've never heard of them ratlling loose to the point that they can be removed before.

The hole you are referring to is an emissions passage. Don't worry about it. I actually passed Texas emissions with headers on my car with that hole plugged up.

I don't know what to tell you in regards to why the car won't run right. It could be the sleeve not fitting back in properly and not allowing a free movement of exhaust gasses but I can't tell without seeing it.