what causes rough running and misfires in my Toyota Highlander Fourth Generation (2020-present)?

Solution

1. Preparation

• Gather tools and parts required for repair.
• Disconnect the battery before starting work on electrical components.

2. Replace Spark Plugs

• Sub-steps:
  1. Remove the engine cover (if applicable) using a socket set.
  2. Disconnect the ignition coils from the spark plugs.
  3. Use a spark plug socket and ratchet to remove old spark plugs.
  4. Inspect the old spark plugs for wear (replace if necessary).
  5. Gap new spark plugs according to manufacturer specifications.
  6. Install new spark plugs and torque them to the manufacturer’s specifications (typically 13-15 lb-ft).
  7. Reconnect the ignition coils.

3. Replace Ignition Coils (if necessary)

• Sub-steps:
  1. Remove the bolts securing the ignition coils.
  2. Disconnect the electrical connectors from the ignition coils.
  3. Remove the old ignition coils from the spark plug wells.
  4. Install new ignition coils and reconnect the electrical connectors.
  5. Torque the ignition coil bolts to manufacturer specifications.

4. Inspect and Clean Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail (ensure the fuel pressure is relieved before removal).
  2. Inspect fuel injectors for clogs or leaks.
  3. Clean the injectors using a fuel injector cleaning kit.
  4. Reinstall the fuel rail and injectors, ensuring proper sealing.

5. Inspect Vacuum Lines

• Sub-steps:
  1. Visually inspect all vacuum lines for cracks or disconnections.
  2. Replace any damaged vacuum lines with manufacturer-approved parts.
  3. Reconnect any loose connections.