why does my BMW 3 Series E90/E91 (2005-2012) have a rough idle after starting?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical issues.
• Ensure the engine is cool before beginning work.

2. Inspect and Replace Spark Plugs

• Tools Required: Socket set, torque wrench, spark plug socket.
• Remove the engine cover (if applicable) by loosening screws or clips.
• Disconnect ignition coils by pulling up on the connectors.
• Remove the old spark plugs using the spark plug socket.
• Inspect the old plugs for wear; replace with OEM or equivalent spark plugs, torqued to the manufacturer's specification (usually around 15 ft-lbs).
• Reinstall ignition coils and reconnect the connectors.

3. Clean Throttle Body

• Tools Required: Throttle body cleaner, soft cloth, screwdriver.
• Disconnect the throttle body electrical connector.
• Remove the throttle body from the intake manifold by loosening the mounting bolts.
• Clean the throttle plate and surrounding areas with throttle body cleaner and a soft cloth.
• Reinstall the throttle body, ensuring proper gasket placement and torque to specifications.

4. Inspect and Clean MAF Sensor

• Tools Required: MAF cleaner, small screwdriver.
• Disconnect the MAF sensor electrical connector.
• Remove the MAF sensor from the air intake duct.
• Spray MAF cleaner onto the sensor elements and allow to dry completely.
• Reinstall the MAF sensor and reconnect the electrical connector.

5. Test Fuel Pressure

• Tools Required: Fuel pressure gauge.
• Locate the fuel rail test port and connect the fuel pressure gauge.
• Turn the ignition to the ON position (do not start the engine) and check the pressure; it should match manufacturer specifications (typically around 50-60 psi for most BMWs).
• If pressure is low, inspect the fuel pump and filter for issues.