After reading your comments it sounds like I may have a bad BPV. I haven't driven the car in a few months so I don't know how long it's been doing this I have a 04 cooper s 15% pulley CAI borla exhaust and renntech software with 47000 on it. I'm only getting 10 to 12 PSI of boost and at idle 10 to 15 in of vac. in was pushing 20 psi and about 25 in of vac. The other thing is when it gets to 10 psi the belt starts to squeaks. Other then that the car is running great. Should I be looking at the BPV or the SC?

 

Hi. I'm now looking into this as well... last few weeks the car has been around 15 psi boost at WOT and 18-24 in Hg. Now, today, I'm at 7-9 psi and 8-10 in Hg. Gauges being used are Defi. What did you end up finding R.C.? Anyone else have input for the cause of this loss of air? Thanks.

 

when the car is off is the valve closed? and that is the position i should zip tie it in ?