why does my BMW 3 Series G20/G21 (2019-2024) have a rough idle when cold?

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Ensure the vehicle is on a flat surface and the engine is off.
• Disconnect the battery to prevent accidental electrical shorts.

Tools Required:

• OBD-II scanner
• Socket set
• Torque wrench
• Multimeter
• Fuel pressure gauge

2. Inspect and Replace Spark Plugs

• Remove the ignition coil covers to access the spark plugs.
• Use a socket wrench to carefully remove the old spark plugs.
• Inspect the spark plugs for signs of wear or fouling.
• Install new spark plugs, ensuring they are gapped correctly to manufacturer specifications.
• Torque the spark plugs to the recommended specification (typically around 15 lb-ft).

3. Fuel System Inspection

• Check the fuel pressure using a fuel pressure gauge. It should be within the manufacturer’s specified range (usually around 50-60 psi).
• If pressure is low, inspect and replace the fuel filter.
• Test the fuel pump operation by listening for the pump's priming sound when turning the ignition on.
• Replace the fuel pump if it is not functioning properly.

4. Clean Throttle Body

• Remove the intake duct to access the throttle body.
• Use throttle body cleaner and a soft cloth to clean the throttle plate and surrounding areas.
• Ensure that the throttle body operates smoothly without any obstruction.
• Reinstall the intake duct and ensure all connections are secure.

5. Verify Coolant Temperature Sensor

• Disconnect the ECT sensor connector.
• Use a multimeter to check resistance and compare it with manufacturer specifications at various temperatures.
• Replace the ECT sensor if readings are outside the acceptable range.