I just pulled the EGR valve with the intent of cleaning it. I noticed at this pont that appying vacuum with no sensor on top will have no effect, since there's a gaping hole right into the chamber where the vacuum is routed.

Anyway, EGR is off and is remarkably clean, including the tube from the exhaust manifold. I can push it open and closed very smoothly, with no obvious signs of any obstruction. I suppose I'll just make sure everything's clean and reassemble.

 

Rust and carbon will accumulate in the exhaust tube going to the EGR and can get stuck in the EGR, keeping it from closing all of the way. While this tube is disconnected from the EGR, start the engine momentarily to blow any accumulation out of the tube.