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

Solution

1. Preparation

• Gather necessary tools and parts for the repair.
• Disconnect the negative battery terminal to ensure safety during repairs.

2. Replace Spark Plugs

• Tools Required: Spark plug socket, torque wrench, ratchet.
• Remove the ignition coils by unscrewing the retaining bolts and gently pulling them out.
• Using a spark plug socket, remove the old spark plugs.
• Inspect the new spark plugs for the correct gap (typically 0.028-0.032 inches for BMW).
• Install the new spark plugs by hand, then torque to the manufacturer’s specification (around 18-22 ft-lb).
• Reinstall the ignition coils, securing them with the retaining bolts.

3. Inspect and Replace Ignition Coils (if necessary)

• Tools Required: Ratchet set, torque wrench.
• If any ignition coils were found faulty during diagnostics, remove the defective coils.
• Install the new ignition coils and secure them with the retaining bolts.
• Ensure all connectors are firmly attached.

4. Check and Replace Fuel Injectors (if necessary)

• Tools Required: Fuel injector puller, ratchet set, torque wrench.
• Disconnect the fuel rail from the fuel injectors.
• Remove any retaining clips and pull out the faulty injectors.
• Install new fuel injectors, applying a small amount of engine oil to the O-rings for a proper seal.
• Reattach the fuel rail and secure it with the specified torque (generally around 10-15 ft-lb).

5. Inspect Vacuum Lines and Intake Manifold

• Tools Required: Visual inspection tools, vacuum gauge (if needed).
• Visually inspect all vacuum lines for cracks or disconnections.
• Check the intake manifold gasket for signs of wear or leaks and replace it if necessary.