What is...

[MikePic]

block off plate, where are they located

[ShdwMastr]

The block the EGR?

[Fast Eddie]

They install on the back (Facing firewall) of your intake manifold.

[Snortin93]

They allow you to remove the EGR (Exhaust gas recirculation) valve. This thing spews unburned exhaust gases back into the intake. Blocking it off will leave the exhaust where it belongs, in the exhaust system. Many people that have done it have noted that the insides of their intake plenum is much cleaner since now it's just fresh air and fuel being burned. The bonus is that it's supposedly much easier to remove and replace the intake plenum when changing rear spark plugs. Many people do it as part of their vacuum reduction, eliminating many hoses that could possibly cause vacuum leaks.

I'm planning on doing the whole thing in the next few weeks.....(but I've been saying that for awhile now. :o )