Does it have a sensor attached? Most without you can blank off. I took mine out and cleaned with carb cleaner before as I figured it must restrict breathing. I've found oven cleaners remove it well, but can strip a metals finish if you're not careful.

The stuff is meant to be combusted though as the EGR actually let's the gas through to be burnt. The deposits are the build up of shit that happens when it's closed mostly if I understand correctly.