We had a problem with the throttle twist grip on our EC130 when it was first delivered. Not sure if it's the same setup as the 120 but the 130 has a sleeve inside the collective tube that is connected to the twist grip, it is a very close fit inside the tube and it rotates along with the twist grip. We found that when they had installed the manual cargo hook release lever on the collective tube, the clamp had 'crushed' the tube ever so slightly at the exact same point where the sleeve was located inside the tube. When I tried to open the throttle I noted that significant force was required to open it, it should normally spring to the full throttle position once you take it off the idle position. They moved the hook release lever down the tube a bit and all was fixed.
CH.