why does my Toyota Highlander Fourth Generation (2020-present) have a rough idle when cold starting

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to ensure safety.

2. Address Engine Codes

• Tools Required: OBD-II scanner
• Use the OBD-II scanner to retrieve and note any error codes.
• Clear the codes after taking notes to reset the system and see if they return.

3. Inspect and Replace Spark Plugs

• Tools Required: Socket set, torque wrench
• Remove the ignition coils by unscrewing them.
• Extract the spark plugs using a spark plug socket.
• Inspect and replace any worn or fouled spark plugs with OEM equivalents.
• Reinstall the spark plugs and torque them to the manufacturer specifications (usually around 13-15 lb-ft).

4. Clean Throttle Body

• Tools Required: Throttle body cleaner, soft cloth, screwdriver
• Remove the air intake duct to gain access to the throttle body.
• Spray throttle body cleaner onto the throttle body and wipe it clean with a soft cloth.
• Ensure the throttle plate moves freely and reassemble the intake duct.

5. Check and Replace Engine Coolant Temperature Sensor (if faulty)

• Tools Required: Socket set, torque wrench
• Locate the engine coolant temperature sensor (usually near the thermostat).
• Disconnect the electrical connector and remove the sensor.
• Install a new sensor and reconnect the electrical connector, ensuring proper torque specifications.

6. Inspect Fuel System

• Tools Required: Fuel pressure gauge
• Connect the fuel pressure gauge to the fuel rail.
• Turn the ignition to the "ON" position (without starting) and check for proper fuel pressure.
• If pressure is low, inspect the fuel pump, fuel filter, and related lines for issues.