how to fix rough idle on Honda Civic 9th Generation (2012-2015) when cold?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool down if it has been running.

2. Spark Plug Inspection and Replacement

• Sub-steps:
  1. Remove the engine cover (if applicable) using a socket set.
  2. Disconnect the ignition coil connectors and remove the coils.
  3. Use a spark plug socket to remove the spark plugs.
  4. Inspect the spark plugs for wear, corrosion, or fouling. Replace if needed.
  5. Install new spark plugs to the specified torque (typically around 13 lb-ft).
  6. Reinstall the ignition coils and reconnect the connectors.

3. Throttle Body Cleaning

• Sub-steps:
  1. Remove the intake duct connected to the throttle body.
  2. Spray throttle body cleaner onto a clean rag and wipe the throttle plate and inside the throttle body.
  3. Ensure the throttle plate operates smoothly and is free of carbon buildup.
  4. Reattach the intake duct securely.

4. Idle Air Control Valve (IAC) Inspection

• Sub-steps:
  1. Locate the IAC valve, typically mounted on or near the throttle body.
  2. Disconnect the electrical connector and remove the IAC valve.
  3. Clean the valve with throttle body cleaner to remove any deposits.
  4. Reinstall the IAC valve and reconnect the electrical connector.

5. Fuel Pressure Check

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail.
  2. Turn the ignition key to the "on" position (do not start the engine) and check the pressure reading.
  3. Compare the reading to the manufacturer's specifications (generally around 40-50 psi).
  4. If pressure is low, inspect the fuel pump and filter for issues.