why does my Toyota Highlander Fourth Generation (2020-present) engine misfire when cold

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the battery to ensure safety while working on electrical components.

2. Inspect and Replace Ignition Components

• Sub-steps:
  1. Remove the engine cover if applicable using a socket set.
  2. Disconnect the wiring harness from each ignition coil.
  3. Remove the ignition coils using a socket wrench and inspect for cracks or carbon tracking.
  4. Replace any faulty ignition coils with new ones.
  5. Remove spark plugs using a spark plug socket and inspect for wear or fouling. Replace if necessary with OEM or equivalent parts.
  6. Reinstall spark plugs and ignition coils, ensuring correct torque (typically 15 ft-lbs for spark plugs).

3. Check and Replace Fuel System Components

• Sub-steps:
  1. Remove the fuel pump relay and ensure the fuel system is depressurized.
  2. Connect the fuel pressure gauge to the fuel rail and start the engine to check for proper fuel pressure (usually 40-50 psi).
  3. If pressure is low, inspect and replace the fuel filter if clogged, and consider replacing the fuel pump if necessary.
  4. Reinstall the fuel pump relay and check for leaks around the fuel system.

4. Inspect and Test Coolant Temperature Sensor

• Sub-steps:
  1. Locate the coolant temperature sensor on the engine block.
  2. Disconnect the electrical connector and remove the sensor.
  3. Test the sensor's resistance with a multimeter according to manufacturer specifications.
  4. Replace the sensor if it is out of specification.
  5. Reinstall the sensor and reconnect the electrical connector.

5. Final Assembly and Reconnect Battery

• Sub-steps:
  1. Reattach any engine covers or components removed during the repair.
  2. Reconnect the battery and ensure all connections are tight.