Abstract: Devices are shown and described for attachment to an engine's intake manifold to regulate its vacuum for fuel economy. The device maintains smooth engine operation by employing multiple valves, each of which provides a supplemental flow of air to the intake manifold during a particular engine mode. Thus, during an idle mode one individually settable valve is operative to supply additional air to the intake manifold to maintain its vacuum at a precisely selected level referenced to an engine idle mode while during deceleration, when a high volume of air is needed, a supplemental flow of air is admitted from another valve which opens at a higher vacuum level from the first valve. A third valve is employed to admit supplemental air during acceleration when the other two valves are closed for an improved fuel to air mixture. Several embodiments are shown.