emission control causing rough idle?

Sounds like the EGR valve passages are not clogged but you could still have a leaky valve. Check the manifold vacuum at idle if you have a gauge. If not, dribble a little gas from a primer can into the top of the carb and see if the idle smooths out. If so, you have a vacuum leak somewhere. You can spray Berrymans, WD40, or similar around all the carb and intake gasket surfaces to check for a leak also. I have to disagree with slantsixdan on the mixture part....when the EGR valve is open there is a dilution of the air charge in the intake which will also effect the mixture. My testing has found that an engine designed to run an EGR valve will tend to ping and run richer if the EGR is not working.