The semicircular groove at the back of the intake journal is the…

The semicircular groove at the back of the intake journal is the groove for the EGR, which is packed solid with exhaust soot. It sets a code for "insufficient EGR flow" and can cause the engine to run hot, or even damage the pistons, so it has to be cleaned periodically. Engines with a plastic intake don't suffer from this.

See this pic for the PN for the gasket.
http://www.supermotors.net/vehicles/registry/media/190433

Owner caption January 2005 · Photo 186 of 980