See Figures 1, 2, and 3
This system is found on Legend and Vigor vehicles.
At a predetermined rpm, the ECU energizes the bypass control solenoid. The solenoid opens electrically, allowing vacuum to flow to the control valve diaphragm(s). As the vacuum acts on the diaphragm, the operating lever is moved and the blades of the valve open. This allows the intake air to follow a shorter path, delivering more power at high rpm. When the rpm drops below the trigger level, the signal from the ECU is discontinued, the solenoid shuts off the vacuum and the system reverts to its previous state.
The diaphragm and linkage may be inspected and cleaned with carburetor cleaner if it is not closing fully. The arm should rest on the limit screw with the vacuum hose connected, but the limit screw must not be adjusted; it is set at the factory and should not be changed. Additionally, the diaphragm is part of the bypass valve assembly. If the diaphragm must be replaced, the bypass valve must be removed from the intake manifold.
The control solenoids are located in the and 1986-1990 Legend emission control box, at the rear of the Vigor intake manifold or behind and below the right headlight on 1991-93 Legend. The solenoid may be removed in straightforward fashion by disconnecting the wiring connector and then the vacuum hoses. Make absolutely certain that the vacuum hoses are reinstalled to the proper ports on the valve(s).