I had a similar problem about 5-6 months back, after checking on this forum found it probably was my PCV, done all the tests that people say and the car didn't change so thought it couldn't be the PCV, it got to the point where it was getting on my nerves so bad that I was willing to just throw parts at it so I changed my DV, Cam follower and PCV and the problems never happened since! Id say its your PCV, can change it in 10 mins and only costs about £22, if you have an older rev PCV you might as well change it anyway because it will one day fail