They're all that way. You can thank the EGR system for that. Honestly its really not hurting anything except maybe choking down the runners. When I pulled the valves out of my donor vortec heads to port them I dug through a good 1/4 inch of crude that was lining the walls of the intake ports before I hit the casting. The heads had 203k miles on them. I hate EGR. Like I said its not going to hurt anything, they're all like that but its stupid it even builds up in the first place.