how to fix P0300 random/multiple cylinder misfire in Toyota Highlander Fourth Generation (2020-prese...

Solution

1. Preparation

• Gather all necessary tools and parts before starting.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool completely before working on it.

2. Replace Spark Plugs

• Tools Required: Socket set, torque wrench, spark plug socket, dielectric grease.
• Remove the ignition coil cover if applicable.
• Unscrew the spark plugs using a spark plug socket.
• Inspect old spark plugs for wear; check the gap against manufacturer specifications.
• Install new spark plugs, applying dielectric grease to the threads.
• Torque to the manufacturer's specifications (usually around 13-16 ft-lbs for most spark plugs).

3. Inspect and Replace Ignition Coils

• Tools Required: Socket set, multimeter.
• Remove the ignition coils by unscrewing them and disconnecting the electrical connectors.
• Use a multimeter to check the resistance of each ignition coil; replace any that are out of specification.
• Install new ignition coils, ensuring they are seated properly and reconnect the electrical connectors.

4. Clean or Replace Fuel Injectors

• Tools Required: Fuel injector cleaning kit or replacement injectors, fuel pressure gauge.
• If cleaning, follow the instructions on the cleaning kit; attach it to the fuel rail and cycle it as per the kit's guidelines.
• If replacing, detach the fuel rail and remove the old injectors. Install new injectors with new O-rings.
• Reattach the fuel rail and check for leaks by turning the ignition to the "ON" position without starting the engine.

5. Inspect Air Intake and Vacuum Lines

• Tools Required: Visual inspection tools, smoke machine (if available).
• Check the air intake hoses for cracks or loose fittings. Tighten or replace as necessary.
• Inspect vacuum lines for signs of wear or leaks; replace any damaged lines.