To check EGR: 1. Remove the center vacuum line from the EGR solenoid. With engine off, suck on the hose then the release the suction while listening for a thunk as the EGR closes. This tells you that the valve is free and is closing properly. 2. With the engine at idle, again suck on the hose to open the EGR. A rough idle confirms that the valve is working and that the passages are not clogged. EGR is normally off at idle and at WOT. 3. Hold the suction for a few seconds to check that the diaphragm is not leaking. It should hold the vacuum and continue the rough idle with no bleed down. 4. Hook up a separate vacuum line to the center port of the EGR solenoid. Put the other end in your mouth, next to your tongue. There is no vacuum at idle but you should feel a vacuum pulse when you blip the throttle. Suck on the hose at idle to check that the solenoid is closed. This tells you that the vacuum source and solenoid are working. This completes a functional test of the EGR valve, EGR passages, EGR solenoid, and EGR vacuum lines. There is one other vacuum line which is for vacuum relief when the EGR turns off. Any break in that line will not affect the EGR operation but may introduce dirty air into the EGR vacuum system. Be aware that the vacuum source for the EGR comes from in front of the throttle plate and will produce zero vacuum at idle. The vacuum comes more from the venturi effect when the throttle is opened than from normal intake vacuum.
