335i throttle problem

[Andy70]

hi there after driving on the motorway last week I noticed at about 2500-3000 revs ish a sudden surge in power even when I just touch the throttle, it seems to then hesitate and sort itself out even though I haven't moved my foot. everywhere else in the rev range is fine, if I just floor it or general town driving is fine and smooth. is it possibly a throttle position sensor of some sort? I have had turbos rebuilt recently, so could something be sticking there? plus I have a jb4 box that came with the car, could it be a fault with that? thanks

Andy