2001 Vauxhall Zafira power blackouts/ dead spots in acceloration

hello all, engine managment light came on while back but car still drove fine, after couple of months it;s started to splutter a little, i still use it daily as it is only way of getting to work but it seems to be getting worse, a mate plugged his computer in and it said crank shaft sensor, so just replaced that, no change, now when we plug computer in it says , fuel passive problem, apparently the car is rejecting the petrol or something along those lines. somtimes it will drive fine when warm but then suddenly kick back in with the black spots, if i press accelorator lightley it builds up power normally as opposed to if i put my foot down it wont accelorate, any ideas would be great, i was thinking of changing fuel filter for start but it must be something fairly serious for the engine management to pick up on it. i saw a simalar post and his was sorted changing the coil pack ( fault ignition) although his problem didn't sound exsactley same, thankyou anyway for reading!