So... added a metal intake pipe and ended up with a load of issues!
Found a damaged vac line so replaced that which made it better but still not great. So after some research I worked out the rubber joiners that came with the kit were too soft and squishing under pressure, and the clip that joined the 2 pipes was not air tight. Adding to the list of success, unfortunately I damaged the standard rubber intake taking it off so couldn't put it back on. So last night in an attempt to fix the issues I cut out the damaged part and combined the two.
Seems to have sorted it (touch wood)
Previous owner has now banned me from fiddling!!! haha