westfieldturbo

Got a bit off a prob with my Westfield zetec silvertop turbo it's all mapped and up and running and going well but there's one problem it seems to have extramly slow throttle response not just when driving but even at idle ! You can actually see it in the boost gadge at idle floor the thottle and boost gadge looses vacuum then revs a sec later and I mean a second literally the ECU is a old e48 DTA mapped off a very reputable mapper and very happy with the map ! So not sure if this is a problem with an actual car part or more a mapping issue ! Any ideas very welcome