It's incorrectly set up analog axes. Check this out
Viewing post in Throttle stuck after pressing it once
hi again . i tried setting the trottle axis to -1 but the issue persists. what happens is when i press the trottle button (not analog) trottle increases from 0 until it reaches 100, not instaltly, it's a gradual increase. it as if it sees button down as a analog being pushed . and when i let go of the button nothing happens and the trottle stays stuck at 100 .