Car stopping directly after releasing the throttle button

Hello,

I’ve set a vehicle for my game which is controllable, but I’ve got a problem. Everything works in term of the controls but the car seems to have a too much powerful brake and also when I release W which is the button for throttle the car stops directly at any speed. I’ve made in blender and I used the metric system and I scaled the car to its real version which is 4 meters long. In Ue4 I added a physic body to the car that its weight matches the real one in kg.

My question here is how do you make the car not stopping directly after releasing the throttle button?