It cannot be my HKS actuator. I took the responsibility off of the actuator by unwinding it basically as far as it goes. I went out for a test drive with it like this, so actuator completely wound out and MBC turned off and I had no boost. I then turned the MBC two clicks and its running bang on 10psi. I'm not arguing, but its strange it works! by the way, dunno if this is important, but I'm not running hi/lo boost, fuk that shiz. edit; furthermore, my brother is running the same MBC on his GT4 and we have set it to 15psi and again, we followed the above directions (like in the turbosmart pdf) and it holds his boost spot on, no spikes, no drop off @ high revs - nowt.