The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

Excessive Oil Consumption and Rough Idle on 2017 340i (N55)

0

Chris P. · rep 0 · May 25, 2:58 AM · 1 replies · solved · Question

Vehicle: 2017 BMW 340i

My 2017 BMW 340i, which has the N55 engine, seems to be going through oil much faster than it should. I'm adding a quart every 1500-2000 miles, and sometimes I notice a slight blue smoke from the exhaust on startup. Lately, the idle has also become a bit rough, and I've noticed a slight whistling sound from the engine bay.

I've checked for external leaks, but everything seems dry. The car has about 70k miles on it. Could this be related to the PCV system? I've read about common issues with these engines, especially with oil consumption and vacuum leaks.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:58 AM

0

ClearTheCode admin answer:

Excessive oil consumption and a rough idle on an N55 engine, especially with a whistling sound, strongly suggest an issue with the Positive Crankcase Ventilation (PCV) system. This is a common failure point.

1. Identify the Cause:

  • PCV Valve/Hose Failure: The PCV valve, often integrated into the valve cover, can fail internally, leading to a vacuum leak and allowing oil vapor to be drawn into the intake at an uncontrolled rate. The whistling sound is often indicative of a ruptured PCV diaphragm or a cracked PCV hose.
  • Valve Cover Gasket: While you've checked for external leaks, a failing valve cover gasket can sometimes allow oil into the spark plug wells or other areas, contributing to consumption or misfires.

2. Diagnostics:

  • Listen closely for the whistling sound; it usually originates from the valve cover area.
  • Check for fault codes. A failing PCV system can cause lean conditions, triggering codes like P0171 (System Too Lean Bank 1) and P0174 (System Too Lean Bank 2).
  • Perform a smoke test to definitively identify vacuum leaks in the intake system and PCV hoses.

3. When to See a Shop:

  • If you're uncomfortable performing a smoke test or replacing the valve cover/PCV system yourself.
  • If the issue persists after addressing the PCV system.
  • If the vehicle is experiencing severe misfires, stalling, or significant performance degradation, as a large vacuum leak can impact engine operation and potentially damage other components over time. Addressing this promptly is crucial to prevent further engine issues.
Menu

Help & account