I had the same problem. You have to do the things i will tell you.
1st remove filter box.
2nd remove carbs not completely. Just pull them off so you can see the black small box that goes up and down and the vboost butterfly under it.
3rd turn your key on. You hear 2 wzzzzzzzzz .......wzzzzzzzz
in the first wzzzzzzz the vboost butterfly must be fully open. When the first wzzzzzzz ends and before the second begins(which closes the butterfly) you turn your key off.
Now your vboost logically must be fully open.
Put your finger and try to pull what the cable that comes out from the small black box. If you cant pull nothing then your vboost is full open. In the other hand if you pull more than the small black box cable can then dont worry. The small black box has a screw in the middle. There is also an adjustment screw beneath where the cable of the small black box ends. Adjust them both in that way so that the butterfly will fully open. Dont be confused it is very easy when you see it. I hope i gave you a hint to help you out. Cheers from greece mate