my Toyota Highlander Fourth Generation (2020-present) has a rough idle, especially during cold start...

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool before starting work.

2. Clean the Throttle Body

• Tools Required: Throttle body cleaner, soft cloth, socket set.
• Remove the air intake duct connected to the throttle body.
• Spray throttle body cleaner onto a soft cloth and wipe the throttle body interior to remove carbon deposits.
• Move the throttle plate gently with your finger to clean both sides; ensure it is fully closed before reassembly.

3. Replace Spark Plugs

• Tools Required: Socket set, torque wrench, gap gauge.
• Remove the ignition coils by unscrewing and disconnecting the electrical connectors.
• Remove the old spark plugs using a spark plug socket.
• Install new spark plugs, ensuring they are gapped to manufacturer specifications (typically around 0.044 inches).
• Reinstall the ignition coils and torque them to the specified value (usually around 12-15 ft-lbs).

4. Inspect and Replace Fuel Filter (if applicable)

• Tools Required: Fuel line disconnect tool, wrench set, safety glasses.
• Relieve the fuel system pressure by removing the fuel pump fuse and starting the engine until it stalls.
• Disconnect the fuel lines using the fuel line disconnect tool.
• Remove the old fuel filter and install the new one in the same orientation.
• Reconnect fuel lines and reinstall the fuel pump fuse.

5. Check for Vacuum Leaks

• Inspect all vacuum hoses for cracks or disconnections; replace any damaged lines.
• Use a smoke machine or carburetor cleaner around the vacuum lines while the engine is running to identify leaks.