my BMW 3 Series E90/E91 has a rough idle when starting after it rains, is that normal?

Solution

1. Preparation

• Gather tools and materials: OBD-II scanner, socket set, multimeter, cleaning supplies, dielectric grease.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery before working on electrical components.

2. Inspect and Clean Ignition Components

• Remove Ignition Coils:

  1. Disconnect the electrical connectors from the ignition coils.
  2. Remove the bolts securing the coils to the engine.
  3. Pull the coils out gently to avoid damaging them.

• Check Spark Plugs:

  1. Inspect spark plugs for moisture or corrosion.
  2. Clean or replace spark plugs if they show signs of wear or damage.

• Apply Dielectric Grease:

  1. Apply dielectric grease to the ignition coil connectors to prevent moisture intrusion.
  2. Reinstall the ignition coils and ensure they are securely fastened.

3. Inspect and Clean MAF Sensor

• Remove MAF Sensor:

  1. Disconnect the MAF sensor electrical connector.
  2. Unscrew and carefully remove the MAF sensor from the air intake duct.

• Clean MAF Sensor:

  1. Use a dedicated MAF sensor cleaner to spray the sensor elements.
  2. Allow the sensor to dry completely before reinstalling.

4. Inspect Air Intake System

• Check for Water Intrusion:
  1. Inspect the air filter for moisture; replace if wet.
  2. Ensure the air intake duct is sealed properly and free from cracks.

5. Reassemble and Test

• Reconnect the battery and start the engine.
• Monitor the idle and check for any diagnostic codes after repairs.