OK....is everybody ready???????
The cover in question is part of the EGR (exhaust gas recirculation) system.
Remove the bolts, then the cover, and clean it all out, cause it will be full of soft carbon crap. There is a gasket available, or just use a little sealer.
The way it all works is this........
The exhaust gasses come out of the head (inside, thru passages)at the #6 cylinder, pass thru the 'egr cooler' (which is actually just a hollow space under that cover on the back of the head, by the firewall), then on to the egr valve.
From the valve, the gasses pass thru a pipe to the intake manifold, then thru a passageway in the intake manifold, over to that little chamber under the cover with the 4 bolts. From there the gasses are allowed to flow into the intake manifold so that they can enter ALL 6 combustion chambers.
A properly operating EGR system will actually give you more HP's, and better MPG.
How, you ask???
By helping to control ignition pre-detonation (pinging), allowing you to run 87 octane fuel (cheapest), and with no pinging, the knock sensor won't tell the computer to retard the timing.
I've been running 15* timing for years, on 87 octane, with no problems. I get 17/22mpg.:biglaugh: