Quick one guys…

Whilst I'm building the other engine I'm getting the current car to Stage 0 and I'm having a bit of an odd problem. Current engine idle is fine runs fine doesn't smoke doesn't hesitate, however when I accelerate Either full throttle or mildly the boost will build to wherever it decides to sit depending on acceleration severity nice and quickly but will then drop slightly back and maintain that level. For example if I put my foot down, by about 3000 rpm the boost has built to around about 0.6 bar but will then drop back by about 0.1 bar and stay comfortably at that level through the Rev range. Wastegate is set to open around 4 psi and I have tried fiddling with this pressure a little to see if it makes any difference

Anyone got any ideas what this is? I put a differently tuned ECU in and it quite happily boosted to around one bar so the wastegate despite being stock seems able to hold itself closed so I'm not sure why the Boost seems to be cut back at stock. If I can I'll get a video and put a YouTube link to it as I don't think I'm explaining it very well!

Thanks all!
Si