EGR valves

What kind of car, engine, etc. Specifics would help.

If by any chance it is a Ford 4.6L or one of the newer GM V6 engines, it is entirely possible that a chunk of carbon got stuck in the pintle of the EGR valve and held it open. Excessive flow does not indicate too much flow from an overall standpoint, but rather, it indicates excessive flow for a given situation. If the computer commands it open just a little bit but detects that it is open more than it commanded it to be, the computer will set an excessive flow code.

You may just need to clean the EGR valve. If that doesn't work, just the valve should require replacement.

Spray the pipe and nut down real good with a rust penetrant first (I like PB Blaster) and let it soak for a good 30 minutes or so... it will help the nut spin freely on the pipe when you go to crack it loose. Also, it is best to remove the bolts that hold the EGR valve to the intake manifold when the engine is cold. Removing steel bolts from an aluminum manifold on a warm engine is generally frowned upon as you run a much higher risk of stripping the threads out of the manifold.