An intake manifold tuning (IMT) valve or variable geometry induction system (VGIS) is used to change the intake manifold plenum configuration. When the IMT valve is open, the intake manifold is configured to one large plenum. When the IMT valve is closed, the intake manifold is configured to 2 smaller plenums. The IMT valve improves engine performance at low and high engine speeds depending on the engine load. Ignition 1 voltage is supplied directly to the IMT valve solenoid. The engine control module (ECM) controls the solenoid by grounding the control circuit. The IMT system contains the following components:

Description and Operation

Air Intake System Description

Special Tools

J 23738-A Vacuum Pump

1. Engine running, verify that DTC P0660 is not set.

⇒	If the DTC is set, refer to DTC P0660.

2. Engine running, command the IMT valve ON with a scan tool. The IMT valve vacuum actuator should move to the closed position.

1. Ignition OFF, disconnect the vacuum hose at the vacuum actuator.
2. Connect a J 23738-A to the port of the vacuum actuator. Apply 51 kPa (15 Hg) of vacuum to the vacuum actuator. Verify the vacuum actuator moves, and that the vacuum remains steady.

⇒	If the vacuum actuator does not move, replace the vacuum actuator.

⇒	If the vacuum decreases, replace the vacuum actuator.

3. Disconnect the harness connector at the IMT valve solenoid.
4. Ignition ON, verify a test lamp illuminates between the ignition 1 voltage circuit terminal 1 and ground.

⇒	If the test lamp does not illuminate, repair the ignition 1 voltage circuit for a short to ground or an open/high resistance. Replace the fuse, if necessary.

5. Ignition OFF, connect a test lamp between the control circuit terminal 2 and the ignition 1 voltage circuit terminal 1.
6. Engine running, command the IMT valve solenoid ON and OFF with a scan tool. The test lamp should turn ON when the solenoid is commanded OFF, and OFF when the solenoid is commanded ON.

⇒	If the test lamp is always ON, test the control circuit for a short to ground. If circuit tests normal, replace the ECM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If circuit tests normal, replace the ECM.

7. Connect the vacuum hose to the vacuum actuator.
8. Connect the harness connector at the IMT valve solenoid.
9. Disconnect the vacuum supply hose from the intake manifold.

Important: The vacuum displayed on the J 23738-A should decrease after engine start, and then stabilize.

10. Connect a J 23738-A to the vacuum supply hose. Apply 51 kPa (15 Hg) of vacuum to the vacuum supply hose. Engine running, verify the vacuum decreases.

⇒	If the vacuum does not decrease, repair the restriction, or replace the IMT valve solenoid.

11. Engine running, monitor the vacuum display. Verify the vacuum stabilizes and remains steady.

⇒	If the vacuum decreases, repair the vacuum leak.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.