It could very well be the pcv valve. If you haven't changed it, I recommend that you to. If you shake it and the centre rattles when you do, it might still be good, but might as well replace it, as its only a couple bux for a new one. Also, I had this problem because of the vented rube that connects from the maf hose to the oil filler neck was in place. After a few months, I would notice caked on oil in and around soem of the vacuum lines, especially after I changed the seal between the throttlebody and the turbo. Lots of pressure there, and I noticed that after awhile it sucks excess oil in the tube, as well as inm the throttlebody. When I converted to the TM intercooler kit, I put on a K&N oil breather tube and plugged the maf hole, and haven't had the problem since. So if you are still running the stock filler neck with the hose connected to that and the maf, that could be your problem as well...
HTH
