After three very unsuccessful attempts to get my idle quality issues solved at my local BMW dealer I have decided to start looking for causes of the issue myself. Under the hood there is clearly something leaking (see attached picture). On RealOEM this appears to be the vacuum pump but I am puzzled to see it leaking what appears to be oil.

What is the top line connected to? It's hard to tell without removing anything and I am reluctant to do so while the car is under warranty.

 

well, coming from owning many turbo honda's I can say that yes vacumm does impact idle... but on the other hand vacumm lines have nothing flowing through them but air... if it's a leaky line it can only be a fluid. most likely its not oil could be powersteering fluid. From the picture its too zoomed in but check the powersteering pump and see if that line leads to it. from what i know the car dosent have oil flowing through lines because its not a turbo car and dosent have oil coolers ect.

But on the bright side your under warranty so just let them deal with it. Take it to another dealer if possible.

 

For anyone curious it appears this line goes to the brake booster so I still don't see any reason for anything but vacuum to be in there. I suppose then it could be brake fluid, but I would be rather surprised if that's the case and a warning was not triggered.

 

can you tell 100% sure that there is a leak in th hose or the connection? If not, there is usually oil residue like that all over the engine compartment. dealers arent the cleanest people when working on your car. only you can be meticulous and make sure that any spalshes of oil here and ther are cleaned up. if its what I think it is, then I wouldnt worry about that.

 

Maybe not 100%, but 99% sure. It's the only area I see that's dirty and I can see the fluid beading up at the end of the hose.

 

Hard to tell with that close up shot...but looks like a valve cover breather or (blow by) line to me...they tend to build up oil residue around the connection (from hose to line) but hard to tell with that pic. Don't think you'll see a brake line with steel going into rubber like that...most are stainless into high pressure rubber hose with high pressure connections.

 

From the diagram on the RealOEM link it definitely shows that line connecting to the brake system. I don't think it's a line that should be carrying brake fluid in the first place -- it's the vacuum source, so by definition there shouldn't be anything liquid to leak AFAIK.