why does my BMW 3 Series E90/E91 (2005-2012) have a strange noise when idling?

Solution

1. Preparation

• Gather tools and parts required for repair.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Worn Components

A. Check Engine Mounts

• Remove the engine cover if applicable.
• Inspect the engine mounts for cracks or excessive wear.
• If damaged, use a socket set to remove the bolts securing the mounts and replace them with new ones.

B. Inspect and Replace Serpentine Belt

• Use a belt tensioner tool to relieve tension on the serpentine belt.
• Remove the belt and check for fraying or cracking.
• Install a new belt by routing it according to the belt diagram and ensuring proper tension.

C. Inspect Accessory Components

• Check the alternator, power steering pump, and other accessories for wear.
• Replace any failing components as necessary:
  • For alternator: Disconnect wiring, remove bolts, and install the new unit.
  • For power steering pump: Drain fluid, remove hoses, and replace the pump.

3. Reassemble and Test

• Reattach any covers removed during inspection.
• Reconnect the battery.
• Start the engine and verify that the noise has been eliminated.