Volkswagen Polo car wont rev above 2000rpm

2005 polo 3 cylinder 1.2 sounds like its running on 2 pots instead of 3 pots, will not rev above 2000revs any attempt to get the revs higher result in the rev counter bouncing between 1500 and 2000revs accompanied by a whooshing sound that appears to be the pressure releif valve cutting in and out,however if car started with throttle to floor car will rev up to 5/6000revs albeit erraticlly, but if I drop back to 1500 revs again car wont rev back up past 2000,looked at plugs all clean and gapped and sparking,tried bleeding air from injecter feed bleed valve with ignition on expecting a constant squirt of petrol, but just got a brief squirt of petrol followed by nothing else,is this normal with the ignition on.your ideas will be most welcome thanks,also is there any point in removing the injectors just to see if there all squirting petrol out or is this just pointless . thanks all