Twingo doesn’t really take gas

Hi, everybody! I have a Twingo 16v, Bj2001, 76000km down! When I drove home from work today, I had the problem at the traffic lights when I was speeding up, that I at the same time had the feeling that someone would step on the brakes in a 1-second-stroke. That then pulled up for a while, but then was away again. I still went to Renault and left the car there to check through. I drive a lot of highway and don’t want to go there in the morning at 7 U So, now to my question: Do you have any idea what that could be? Would you like to adjust me to it quite a bit? I still have a guarantee, so I would also be interested in what falls into the guarantee and what is not (electronics stuff). Daaaanke already!