I have a 2010 Clubman that has 140,000 miles on it. For a while, the car has been burning oil, but only after a long period of idling. It would occasionally throw code P0420, and I eventually decided the PCV must be failing (it had never been replaced).
Before I could get around to changing it--I was driving home and the car started shaking, misfiring, and emitting large amounts of dark smoke. I got it home safely and parked it until I could find time to work on it. Two days ago, I replaced the valve cover (integrated PCV), spark plugs, changed the oil, and added high-mileage Seafoam to the tank. The car sounds good, idles smoothly, but still burns bluish smoke after a long idle (5+ minutes). Could this be the Seafoam cleaning out the sludge?

I'm concerned this is a symptom of leaking valve stem seals...I added some Bar's Leaks Oil Seal to see if it helps. So far I haven't driven the ~250 miles they recommend on the bottle, but if it doesn't work...what's the next step? Is there a different possibility I could try, or do I go ahead and take it to my mechanic to replace the valve stem seals? I don't have an engine lift, or I would replace them myself, and my mechanic (the only one I trust) is 120 miles away. If I have to pay up, I will, but if there's an easier solution I would be willing to try it!

 

P0420 is the cat efficiency code, which could be a result of the failing PCV system. Sounds like you changed the right parts to fix the PCV. Remaining smoke could be due to lingering oil in the intake. My next step might be an intake valve cleaning.

 

I definitely will try that! There was a ton of sludge on the spark plugs and on the valve cover itself, so I wouldn't be surprised if the intake needs a good cleaning too.

 

Had another car engine emit lots of smoke from a cold start. Was a bad air/oil separator. Had the AOS replaced then when I got the car back just arranged to drive it in town which got the engine up to full operating temperature and kept it there for the bit of oil in the intake to be drawn into the engine and burned. Subsequent engine starts cold or hot were smoke free.

I wouldn't bother with an intake cleaning unless the intake was loaded with solid deposits