It could be. You need to check it. It should be closed, and there should be no vacuum from the source at idle. The pintle should also make a good seal when it's closed. You can test the valve itself with a known steady vacuum source. IE: any port that has steady vacuum when the engine is running...Or a vacuum pump tool. Disconnect the normal vacuuum hose from the EGR valve, and hook up the known vacuum. The rpm should drop, and you should hear a noticable difference. "Worse running" The main thing is to listen for a difference. If it does change, most likely the valve is good. Clean it, and reinstall. If applying vacuum makes no difference at all at idle, the valve is most likely shot and has a ruptered diaphram or a pintle that is not seating well. As far as the normal vacuum source, modulator, whatever... there should be none at idle, but increase as you give it gas. As long as it does that, it's ok. But it's possible you have other problems. Check fuel filter and flow, make sure it's not starving for gas. "don't forget the strainer in the tank..." Also make sure it's not drowning. Rochesters like to have the float stick...A recent rebuilt "should " be ok, but all it takes is a spec of dirt to cause this. If gas runs all over from the base of the carb, the float/ needle/ seat is sticking. Also you will smell the excess gas. BTW... Make sure no vacuum leaks. Check all rubber hoses, etc. MK