I'm trying t figure out what the rectangle cover is called on the throttle body. I need the gasket.

 

I'm pretty sure it is called a throttle body cover. Not sure if you can purchase the gasket except from the dealer. You could always get some gasket material from an auto parts and make your own.

 

Shoebox has the number for the gasket kit that includes the cover plate gasket and bottom plate gasket. Look at his parts list:

http://shbox.com/1/Parts.htm

 

Cool, thanks.

 

http://shbox.com/1/t_body_kit.jpg

 

What is the point of the throttle body having a cover on it?

 

If it wasn't there, it would allow dirty air to flow into the front of the throttle body, bypassing the MAF sensor.

If you look at the passenger side of the throttle body, where the hose from the passenger side valve cover connects, that passage is open to the chamber on top of the throttle body. Then there is a hole that ends up in front of the throttle blades, in between the bores. The vacuum from the PCV system is supposed to be pulling filtered, MAF measured air through the throttle body, through the hose to the valve cover, and then through the crankcase and lifter valley to purge the piston ring blowby. If blowby gets excessive, the flow can reverse and entrain oil drops as it flows through the valve cover, out the hose and into the top of the throttle body, then into the intake manifold through the throttle body bores. Maybe GM put that chamber there to trap the oil... but if they did, it doesn't do a good job.