Controller anolog stick acting wierd

So playing racing games like Forza or project cars, my left stick is just acting wierd, like sometimes its not detecting full sometimes it's mixes like full then 75%, i mean like I'm turning the analog fully to the left but in the game, I'm only using 75% of my original 100% output to the analog stick, it's my left analog stick and it only affects when I'm going left or whatever the actual saying is, not sure if it's controller drifting because being afk, my camera or character doesn't inch or move up