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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the engine is cool and disconnect the battery.

2. Replace Spark Plugs

• Tools Required: Spark plug socket, ratchet, torque wrench.
• Remove the ignition coils by unscrewing or unclipping them.
• Take out old spark plugs using the spark plug socket.
• Inspect the gap on new spark plugs and set to manufacturer specifications (usually 0.032-0.036 inches).
• Install new spark plugs and torque to specification (typically 15 ft-lbs).
• Reinstall the ignition coils.

3. Inspect and Replace Ignition Coils (if necessary)

• Tools Required: Ratchet, socket set.
• Remove the ignition coil(s) that were swapped during diagnosis if faulty.
• Install new ignition coils ensuring proper seating and connection of electrical connectors.

4. Check and Clean Fuel Injectors

• Tools Required: Fuel injector cleaning kit, fuel pressure gauge.
• Disconnect fuel injector connectors and fuel lines.
• Remove injectors from their seats.
• Clean injectors using a fuel injector cleaning kit or replace them if necessary.
• Reinstall fuel injectors and reconnect all lines and connectors.

5. Repair Vacuum Leaks (if found)

• Tools Required: Vacuum gauge, hose clamps.
• Inspect all vacuum hoses for cracks or disconnections.
• Replace any damaged hoses and ensure all connections are secure.