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