how to fix P0300 random misfire in my BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather tools and materials.
• Disconnect the battery to ensure safety while working on electrical components.

2. Inspect and Replace Spark Plugs

• Remove the engine cover if applicable.
• Use a spark plug socket to remove each spark plug.
• Inspect for signs of wear or damage; replace with OEM specifications if needed.
• Torque new spark plugs to the manufacturer’s specifications (typically around 18-25 ft-lbs).

3. Test and Replace Ignition Coils

• Visually inspect ignition coils for physical damage.
• Use a multimeter to test the resistance of each coil; replace any faulty coils.
• Install new ignition coils by connecting them firmly to their respective spark plug.

4. Fuel System Inspection

• Connect a fuel pressure gauge to the fuel rail.
• Turn the ignition on without starting the engine to check pressure; it should meet manufacturer specifications (usually around 50-60 psi).
• If pressure is low, check the fuel pump and fuel filter for blockages or failure and replace as necessary.

5. Inspect Air Intake and MAF Sensor

• Check all hoses and connections in the air intake system for leaks or cracks.
• Remove the MAF sensor from the air intake piping.
• Clean the MAF sensor with MAF cleaner spray and reinstall it securely.