why does my Toyota Highlander Third Generation (2014-2019) make a hissing noise when idle?

Solution

1. Preparation

• Gather tools and materials.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative terminal of the battery to prevent any electrical shorts.

2. Inspect and Replace Vacuum Hoses

• Sub-steps:
  1. Locate all vacuum hoses connected to the intake manifold and check for any visible damage or signs of wear.
  2. Replace any cracked or disconnected hoses with new vacuum hoses of the same diameter.
  3. Secure all connections tightly to prevent air leaks.

3. Check and Clean the Throttle Body

• Sub-steps:
  1. Remove the air intake duct to access the throttle body.
  2. Use throttle body cleaner and a soft cloth to clean the throttle plate and surrounding area.
  3. Reattach the air intake duct securely.

4. Inspect and Replace Intake Manifold Gasket

• Sub-steps:
  1. Remove any components obstructing access to the intake manifold.
  2. Unbolt the intake manifold, being careful to note the order of removal for reinstallation.
  3. Remove the old gasket and clean the mating surfaces.
  4. Install the new gasket and reassemble the intake manifold, tightening bolts to the manufacturer’s specified torque values.

5. Final Checks

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Start the engine and listen for any remaining hissing noises.
  3. Monitor RPM and check for error codes again using the OBD-II scanner.

Tools Required:

• OBD-II scanner
• Socket set
• Torque wrench
• Throttle body cleaner
• Soft cloth

Parts Required:

• New vacuum hoses
• Intake manifold gasket

Estimated Repair Time: 2-4 hours

Safety Warnings:

• Disconnect the battery before working on electrical systems.
• Allow the engine to cool before working on the intake components.