Mysterious vacuum leak can = Bad PCV
 

So I've been pulling my hair out recently trying to figure out why my TI wouldn't idle smoothly and kept giving me a check engine light.

The codes were:
pre-cat 02
fuel trim multiplicative

After replacing my pre-cat 02, and cleaning my MAF the problem still processed. I noticed my water pump was leaking so while I replaced it I decided to completely replace every hose under the hood also. I put in all new gaskets, spark plugs, and wires. The problem was still there! I checked the TPS, idle control valve, coolant temp, replaced the fuel filter, and still nothing!

Finally a senior BMW tech gave me a very good tip. With the car running (attempting to idle) remove the oil cap. If you notice allot of suction when removing it, or a change in the idle then, the PCV valve is stuck open. This creates an elusive vacuum leak. Sure enough that was my problem! :smile:

Awesome Tip!!!!

I had a rough idle & threw lots of codes P1174, all the misfire codes, cam position sensor, TPS and a few more for good measure. Checked all the rubber lines to find the crankcase vent hose going to the PCV valve disinigrated. Replaced it and the vacuum in the crankcase was so high it sounded like turbos spooling. Read your post & all is well again. $58 w/ CCA discount for a PCV valve, 2 cookies & a capuchino. :smile:
Thanks a bunch!

Great tip thanks

Awesome. I think this is my squealing problem. I took the oil cap off today and it stopped squealing. It was difficult to take off while running. Lots of vacuum.