Hey all, I'm new to the forum and have been researching an issue with my Mini cooper running rough at idle. It doesn't seem to happen all the time and I am not getting any codes or check engine lights, but this is new this winter. I've also noticed that when I have the car parked and running, if I remove the oil fill cap, I can hear a sucking/vacuum sound coming from the cap when I open it. I suppose this could be normal and I just didn't notice it before, but don't recall opening the oil cap when the car was running. In my research, I found that a sucking sound from the oil cap could be a problem with the PCV value, but I can't for the life of me figure out where that might be on this car. Is it hidden/built within the valve cover? Any help is appreciated.

Tim

 

Do you have the base F55 with the 3 cylinder? We have 2016 F57 convertible with the 134hp 3 cylinder and it can be rough on start-up. Also not sure if it is a good idea to remove the oil cap when the car is running.

 

Yeah,

This is the base F55 with 3 cylinders. And you are probably right, I don't normally open the oil cap when the car is running, but it was to check for a "sucking" sound that is characteristic of a failed PVC... but being this is a 3 cylinder, maybe the vacuum inside the engine is normal?

 

If you have no codes, I would be looking at mounts. The front mount is a known weak link on the S models, might also be an issue on the 3 cylinder turbo.

 

Thanks, I will check that out. I'm learning more about minis than I care to admit. Lots of service personality...

I hope to get some quality inspection time on it this weekend since its my wife's daily driver.

 

The PCV system sounds like it is working normal to me. At idle and any time the intake system is under negative pressure, the PCV system should be pulling said vacuum on the crankcase. When you go into boost, the PCV valve should act as a check valve and prevent pressurizing said crankcase and blowing out gaskets. At least that is how PCV systems worked, as I haven't had to dive into how PCV systems on todays cars work with all the additional control that is now being exercised.

So, when you open up the oil filler cap, you are basically opening up a vacuum leak to the PCV system and that could certainly trigger a rough idle. The air pulled in through the filler cap hole is un-metered through the MAF sensor and creates 'confusion' to the ECU.