While the car's running, reach under the top of the valve and manually pull the diaphragm up (or use a vacuum pump on the nipple on the top of the valve). If the car's idle stumbles or the engine dies, the passageways are fine, and you may have a bad valve OR apply solenoid.
If the solenoid's bad (and they're not that great of a solenoid) just bypass the solenoid and run a line directly to the EGR valve's vacuum port from the port on the throttle body.
If the car doesn't die and idles fine, you've got plugged EGR passageways in the intake manifold, and you're looking at some serious R&R work.
