This has been a ongoing issue for about 2 months now. I took my car to the dealer because I was getting a violent hesitation. Trac cntrl, and CEL came on.

The dealer found that there . I asked the service writer if it needs a new hose, and he said no. Now I'm having the same issue.


Near the BPV:
There is a y fitting that has 3 hoses connected to it. 1- goes to the air box, 2- goes into the BPV, and 3 I have not a clue. I'm assuming that this mystery hose is the problem. I'm clueless at this point.

 

Check your hoses...someone I know had the same problem...found out that something got under the engine bay and chewed on the hoses...could be a mouse. Good luck!

 

My '05 R53 coughed for a bit (a few miles at appx. 60 mph) while on a trip over to the coast last week. As I was already scheduled for an appointment at the local British car specialist in SLO, for a completely unrelated item, I asked the technician to check the computer for any codes. He found it to show there was a vacuum leak, of some sorts, somewhere in the system. Upon his suggestion, we smoke tested the car. What was found was a crack, in a factory plastic weld, in the plastic tube that connects between the supercharger and the throttle body. Lots'a trouble to get to it for a fix, but inevitable that it needs to be done.

If you haven't already done so, it's worth the money I spent to have someone smoke test your car to pinpoint the exact location of your leak. Best of Luck in your search!

 

If you have not figured it out yet as for the Y...the bpv has 2 nipples in which is supposd to be sealed off when no vaccum line is attached(jcw air box). the hose on the bpv is cut, y nipple placed in connection of 2 ends, and air box vac line to the 3rd nipple.