Volkswagen Passat B8 (2015-2022) rough idle when cold start, what could be wrong?

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to avoid electrical shorts.
• Allow the engine to cool down completely before starting work.

2. Clean the Throttle Body

• Tools Required: Throttle body cleaner, soft cloth, screwdriver set.
• Remove the air intake duct to access the throttle body.
• Spray throttle body cleaner into the throttle body while moving the throttle plate open and closed to remove carbon deposits.
• Wipe clean with a soft cloth and ensure no debris falls inside.
• Reinstall the air intake duct securely.

3. Inspect and Clean Fuel Injectors

• Tools Required: Fuel injector cleaner kit, appropriate sockets.
• Disconnect the fuel injector connectors and remove the fuel rail assembly.
• Use a fuel injector cleaner kit to clean the injectors as per the manufacturer's instructions.
• Reinstall the fuel rail and reconnect the fuel injector connectors.

4. Check for Vacuum Leaks

• Tools Required: Vacuum gauge or smoke machine.
• Inspect all vacuum hoses for cracks or disconnections.
• If using a smoke machine, introduce smoke into the intake system and look for smoke escaping, indicating a leak.
• Replace any damaged hoses or components.

5. Inspect Engine Oil

• Tools Required: Oil wrench, oil filter wrench.
• Check oil level with the dipstick and ensure it is at the proper level.
• If oil is dirty or low, perform an oil change using the recommended oil type for the Passat B8.
• Replace the oil filter if necessary.