I had the same problem and still do ATM but car is off the road now. I knew i had a dodgy Fuel Pump cos it was running lean, and then all this started to happen, So i now have a new/bigger fuel pump and also a Z32 AFM being installed this week which should sort the problems out. I have also heard that the pipeing could also be a issue, but i'd start with the fuel pump if i was you!