1999 Buick Century erg port

Unbolt the EGR from the intake manifold. I'm not sure about this engine, they're in different places, and the port is configured differently. You'll need cleaner, a small stiff brush, a short piece of soft wire, and perhaps a piece of coathanger or tool to dig out carbonized gunk. Probably the worst problem is not in the EGR itself but in the manifold, which sometimes must be removed to unclog. Use the wire as a probe to make sure it's clear. I've seen them look open but still obstructed farther inside. Check the exhaust riser as well.