emission control causing rough idle?

Fair enough. However, you would still be best served by a proper diagnosis. Without that, you are merely guessing that the EGR valve is bad. It is fairly easy to diagnose. Simply verify you have vacuum to the valve at part throttle with a vacuum gauge. Once verified, pull a vacuum on the EGR valve and see if it opens. If it fails to open, then the dashpot is ruptured. If it seems to open, you can diagnose further by removing and inspecting the valve to make sure it is closed completely. Carbon buildup caked around the orifice will cause a manifold vacuum leak and the rough idle condition. You might can get by with cleaning it and putting it back on and all is well. You never know. Either way, at least if you diagnose it, not only will you learn something, but you will find the problem.