How to test EGR valve solenoid on Chevy El Camino 305 high NOx

I checked the EGR valve by hooking a vacuum hose to direct manifold vacuum. The RPM drop was very little. Does this mean the manifold is plugged? The reason I'm doing this is because my Chevy El Camino has high NOx. I have a new EGR valve. I don't want to remove the intake manifold unless I really have to. Is there a way I can try to clean it out without removing it? The smog tecehnician said I should also check the air injection tubes. Do I have to inspect the Air Injection system as well?

Answer:		The lack in RPM drop may indicate plugged passages. You can remove the EGR valve and try using a long thin brush and carburetor cleaner to clean it out as much as possible without having to remove the intake manifold. The EGR valve solenoid should energize when the engine is off throttle at around 15%. Check the power wires to the solenoid for 5 volts when it's supposed to be activated. A faulty air injection system can cause high NOx as well. Insure the AIR injection system is only diverting air into the exhaust manifold during cold startups. posted by SmogTips Support