Bank 1 Lean - need sanity check before I waste money
Thread Starter
Junior Member
Joined: Mar 2014
Posts: 18
Likes: 0
2009 C63 AMG
Bank 1 Lean - need sanity check before I waste money
I am getting a CEL for Bank 1 Lean. This happened to me about 9k miles ago and it was the PCV valve. I believe it is the same issue again. The oil dipstick is under vacuum, I can hear it when I pull the dipstick out and the cars idle increases. It also appears that the oil filler cap is under vacuum, The idle speed jumps up when I remove the filler cap. For the mechanics out there, does it sound like PCV again to you. I am kind of surprised it would need replacement again so soon. Other than a tune and ROW air boxes, it is stock.
Super Member
Joined: Apr 2010
Posts: 609
Likes: 38
From: Arizona
2011 C63
Under normal conditions the PCV system will pull a slight vacuum on the engine crankcase. However, if the PCV valve sticks open or the spring breaks, it can pull too much crankcase air into the engine inlet causing it to lean out. Before you fix it, just look really hard for other sources of a vacuum leak.
Thread Starter
Junior Member
Joined: Mar 2014
Posts: 18
Likes: 0
2009 C63 AMG
Thanks for the advice. I tried spraying brake cleaner around known leak areas that others have mentioned but didn't notice any change in the idle speed. The thing that has me most curious is the abrupt idle change when I remove the oil filler cap. You can feel the vacuum pulling on the cap and once it is lifted up a bit, the idle speed increases by a few hundred rpm immediately.
Super Member
Joined: Apr 2010
Posts: 609
Likes: 38
From: Arizona
2011 C63
Thanks for the advice. I tried spraying brake cleaner around known leak areas that others have mentioned but didn't notice any change in the idle speed. The thing that has me most curious is the abrupt idle change when I remove the oil filler cap. You can feel the vacuum pulling on the cap and once it is lifted up a bit, the idle speed increases by a few hundred rpm immediately.
). I can hear a vacuum sound and the idle speed raises by around 100 to 200 rpm (tough to tell using the stock tach).
MBWorld Fanatic!
Joined: Feb 2010
Posts: 5,649
Likes: 484
2012 C63;1971 280SE 3.5(Sold);2023 EQS 450 SUV 4 Matic (Wife's)
There should be a way for metered air (downstream of the MAF) to enter the crankcase to balance the air drawn from the crankcase through the PCV. Maybe that line is plugged or pinched causing vacuum to build in the crankcase. Not sure where it is located on our cars.
