Engine Rattle or Buzz Noise Between 1600-3800 RPM - keywords intake IMTV LZ9 manifold tuning valve

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some owners may comment about an engine rattling or buzzing noise while driving with engine RPM between 1600-3800.

To obtain optimum torque and horsepower, the Intake Manifold Tuning Valve (IMTV) is fully closed between 1600 and 3800 RPM. If the IMTV valve blade-to-drive motor coupler is worn or loose, and the IMTV valve is commanded closed, a buzzing or rattling noise may result.

In most instances, this noise will never be audible to the customer, as in durability testing it was discovered only when the engine compartment hood was open while standing next to the vehicle.

To determine if the IMTV valve is the source of the concern, perform the following steps:

1. Open hood of the vehicle.
2. Using a Tech 2, command the IMTV valve fully closed.
3. Raise the engine RPM to between 1600-3800 RPM.
4. If noise is duplicated, command the IMTV to the open position. If noise is gone, replace the IMTV valve assembly.
5. If noise was not eliminated in the above test, review service information for other sources of engine noise and perform further diagnosis.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.