Pickup & 4RUNNER: Federal

Check condition of all hoses and tubes. Remove hose from air switching valve. Verify bubbling noise is heard from air switching valve at idle.
Disconnect vacuum hose from air switching valve. Bubbling noise should not be heard from air switching valve at idle. Reconnect vacuum hose and air suction hose.
To check vacuum control valve, race engine and quickly close throttle valve. Bubbling noise should stop momentarily. If system does not operate as indicated, check system components.

Fig 1: Air Suction System (Pickup and 4Runner - California)

Fig 2: Air Suction System (Pickup and 4Runner - Federal)