my BMW X3 F25 (2011-2018) has a rough start when cold what could be causing this

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the vehicle is parked on a level surface and secure.
• Disconnect the negative battery terminal for safety.

2. Inspect Battery and Connections

• Tools Required: Multimeter, socket set
• Check the battery voltage; it should be above 12.4 volts.
• Clean battery terminals and ensure tight connections.

3. Replace Spark Plugs and Ignition Coils (if necessary)

• Tools Required: Spark plug socket, torque wrench, ratchet
• Remove the ignition coil by unbolting it and disconnecting the electrical connector.
• Remove the spark plug using a spark plug socket.
• Install new spark plugs, ensuring they are gapped correctly to manufacturer specifications (typically around 0.032 inches).
• Reinstall the ignition coil and torque to manufacturer specifications (usually around 10 Nm).

4. Check and Replace Fuel Filter (if clogged)

• Tools Required: Fuel line disconnect tool, socket set
• Relieve fuel system pressure by removing the fuel pump fuse and starting the engine until it stalls.
• Disconnect the fuel lines using a fuel line disconnect tool.
• Remove the fuel filter and replace it with a new one, ensuring flow direction is correct.

5. Inspect and Clean the Air Intake System

• Tools Required: Screwdriver set, cleaning cloth
• Remove the air intake duct and inspect for dirt or obstructions.
• Clean the air filter and replace if necessary.

6. Test and Replace Coolant Temperature Sensor (if faulty)

• Tools Required: Socket set, multimeter
• Locate the coolant temperature sensor and disconnect the electrical connector.
• Test the sensor resistance with a multimeter against manufacturer specifications.
• If the sensor is faulty, replace it and reconnect.