Why would my car accelerate quicker with less gas?

Quick question -I have a Peugeot 308 (UK, petrol, 1.6L) that has been slowing down gradually for a few months. I seemed to be losing power and therefore was adding more gas, which caused the engine to make a loud noise, but the revs/speed to not increase.Recently however I have discovered that there is an amount of gas I can apply which will cause the car to accelerate as it used to. For example in the range of 20-30% throttle, I appear to have a full range of power, anything above this just causes engine noise and no extra response.I've taken the car to a few garages and none of them seem to have understood the problem and therefore couldn't find a fix.Has anyone encountered this problem before?Cheers! via /r/cars http://ift.tt/2twl6w9