Sure its not a boost leak? I remember when I modded my airbox to have a solid 2.5" cold intake pipe. At the end of the pipe I had a cone filter and removed the panel filter. What I ended up with was huge flutter and hardly and high end power. Turns out the box filter is designed in a manner where it make the air box air tight, because it wasn't air tight I was getting inconsistent readings on the MAF and couldn't work out wtf was going on and under high end it just felt rubbish. Drank fuel like it was in the desert too, 3mile trip cost me £10.
So it seems like a leak, but I'd still look over the system as well just encase its not just the actuator (TIP and vacuum hosing). Also get the forge actuator, a real good piece of kit to replace the OEM one.
