With the engine warmed-up at idle apply vaccum to the nipple on the EGR,
The idle should become rough until the vacuum is removed. If this goes as described the valve and plumbing are good.
The ECU tests the EGR when the engine is warm and decelerating by applying vacuum to the valve, at the same time it monitors intake manifold vacuum and looks for a change while the valve is open,It does this through the manifold pressure sensor in the ignition control unit.
Replace the rubber vacuum hoses to the ignition control!
Mike