A vacuum sustaining valve (VSV) for temporarily sustaining at least some engine intake manifold vacuum to an EGR valve when engine intake manifold vacuum falls below a predetermined value. The VSV has an inlet port, an outlet port, and a flow path between the two ports. A check valve is disposed with the flow path and is selectively positioned in accordance with manifold vacuum. When manifold vacuum is above a predetermined magnitude, the check valve is positioned to allow bi-directional flow between the two ports. When manifold vacuum is below the predetermined magnitude, the check valve is positioned to function as a check that allows vacuum to pass from the inlet port to the outlet port, but not in the opposite direction.