My 2.5 v6 has an annoying 'flat-spot' when accellerating at just under 3000rpm. Once over this point she pulls like a mule. Is this likely to be caused by the VIS valve problem I've read about? If it is a possible cause, then is there anything I can do to confirm this without having to actually break open the VIS valve as per the instruction I've seen in the 'How To' section? Any ideas.
