Player direction in air

That's a hard question to answer without more information on how your car is made. If it was a rigidbody you can stop that with

 private var grounded = false;
 // This part detects whether or not the object is grounded and stores it in a variable
 function OnCollisionEnter ()
 {
     state ++;
     if(state > 0)
     {
         grounded = true;
     }
 }
  
  
 function OnCollisionExit ()
 {
 state --;
     if(state < 1)
     {
         grounded = false;
         state = 0;
     }
 }
 
 function FixedUpdate ()
 {
 
 if (grounded == false) {
 rigidbody.freezeRotation = true; }}

I have some errors with the script after I added it to it.

  var speed : float = 8.0;
     var jumpSpeed : float = 9.0;
     var turnSpeed : float = 90;
     
     private var moveDirection: Vector3 = Vector3.zero;
     private var distGround: float;
     private var isGrounded: boolean = false;
     private var grounded = false;
     
     function Start(){
         rigidbody.freezeRotation = true; // disable physics rotation
         var caps: CapsuleCollider = transform.collider;
         distGround = caps.height / 2 - caps.center.y; // distance to ground
     }
     
     function Update(){
         var hit: RaycastHit; // use raycast to check if character grounded
         isGrounded = Physics.Raycast(transform.position, -transform.up, distGround + 0.1);
         if (isGrounded && Input.GetButtonDown("Jump")){ // only jump from the ground
             rigidbody.velocity.y += jumpSpeed; 
         }
         // rotate character and define direction to move
         transform.Rotate(0, Input.GetAxis("Horizontal") * turnSpeed * Time.deltaTime, 0);
         moveDirection = -Vector3.forward * Input.GetAxis("Vertical") * speed;
     }
         // This part detects whether or not the object is grounded and stores it in a variable
         function OnCollisionEnter ()
         {
             state ++;
             if(state > 0)
             {
                 grounded = true;
             }
         }
         
         function OnCollisionExit ()
         {
         state --;
             if(state < 1)
             {
                 grounded = false;
                 state = 0;
             }
         }
     
     function FixedUpdate(){ // move at FixedUpdate to get stable results
         transform.Translate(moveDirection * Time.deltaTime);
     }
     {
     
     if (grounded == false); {
     rigidbody.freezeRotation : true; }}

can you help me?

I have also another problem that says $$anonymous$$ identifier: 'state' how can I fix it?

my bad i forgot a state variable.

add private var state = 0; to your code to fix that error.

That whole part of the code was to store grounded to a variable but looking at your script it seems like you already have one. so take out the extra junk that stores the grounded variable and just change the (grounded to (isGrounded on the freeze rotation command.

it didn't work. and I have a error when I am changing a little bit in the code that says unexpected identifier 'if'