Making an effective Airdash

I've just recently started using Unity3D and it's truly, for lack of better words, awesome. It's almost like a toy box with an unlimited amount of toys.

Anyway, I've been through a few tutorials on 2D platforming controls, and I've applied what I know so far on an innocent cube. But I wanted to add something else to it: an Airdash. I have somewhat of an idea on how to implement it, but my idea currently results in the cube hovering in the air for as long as the WaitForSeconds last.

What I basically want to do is have it to where JS sees that I am FIRST holding either left or right and when I press a dash button (X), I go in the held direction for a certain amount of time without being affected by gravity or letting go of the button. Imagine a Megaman X2 or Marvel vs Capcom airdash.

Excuse the code for being messy. I plan on fixing it once I have the basics implimented.

Any ideas or corrections would be most helpful. Thank you.

 @System.NonSerialized
 private var jumpCount : int = 0;
 
 @System.NonSerialized
 private var gravity : float = 35.0;
 
 @System.NonSerialized
 private var gravenabled : boolean = true;
 
 @System.NonSerialized
 private var inAir : boolean = false;
 
 @System.NonSerialized
 private var velocity : Vector3;
 
 @System.NonSerialized
 private var walkSpeed : float = 7.0;
 
 @System.NonSerialized
 private var runSpeed : float = 15.0;
 
 @System.NonSerialized
 private var jumpSpeed : float = 7.0;
 
 @System.NonSerialized
 private var airdashcount : int = 0;
 
 @System.NonSerialized
 private var airdashspeed : float = 40.0;
 
 class characjump {
 
 @System.NonSerialized
 var height: float = 30.0;
 
 @System.NonSerialized
 var doubleheight: float = 15.0;
 
 @System.NonSerialized
 var verticalSpeed: float = 0.0;
 }
 
 var charjump : characjump;
 
 private var moveDirection : Vector3 = Vector3.zero;
 
 var controller : CharacterController;
 controller = GetComponent(CharacterController);
 
 function Move (){
 var h = Input.GetAxisRaw("Horizontal");
 var v = Input.GetAxisRaw("Vertical");
 var airdash: boolean = false;
 var doubletap: float = 0.5;
 var lastTime: float = 0.0;
 var running: boolean = false;
 var moving: boolean = false;
 var canControl: boolean = true;
 
 var isMoving = Mathf.Abs(h) == 1;
 
 
 
 if (controller.isGrounded)
 {
 if (Input.GetKey(KeyCode.DownArrow)||Input.GetKeyUp(KeyCode.LeftArrow) || Input.GetKeyUp(KeyCode.RightArrow))
 {
 moveDirection.x = 0;
 }
 else if (Input.GetKey(KeyCode.LeftArrow) || Input.GetKey(KeyCode.RightArrow))
 {
 moveDirection.x = h;
 moveDirection = transform.TransformDirection(moveDirection);
 moveDirection.x *= (running ? runSpeed : walkSpeed);
 }
 }
 
 else
 {
 if (Input.GetKey(KeyCode.X) && !controller.isGrounded && isMoving)
 {
 airdash = true;
 }
 
 if (airdash && airdashcount == 0){
 
 gravenabled = false;
 moveDirection.x = h;
 moveDirection.y = 0;
 moveDirection = transform.TransformDirection(moveDirection);
 moveDirection.x *= airdashspeed;
 
 yield WaitForSeconds(.3);
 
 gravenabled = true;
 airdashcount = 1;
 }
 
 else
 {
 moveDirection.x = h;
 moveDirection = transform.TransformDirection(moveDirection);
 moveDirection.x *= jumpSpeed;
 }
 }
 }
 
 function Jump ()
 {
 var jump = Input.GetKeyDown(KeyCode.Z);
 var fastfall = Input.GetKeyDown(KeyCode.DownArrow);
 if(!controller.isGround)
 {
 inAir = true;
 }
 
 if(jump)
 {
 
 jumpCount +=1;
 
 
 if (jumpCount == 0)
 {
 moveDirection.y = charjump.height;
 }
 else if (jumpCount == 1)
 {
 gravenabled = true;
 moveDirection.y = charjump.doubleheight;
 gravity = 35.0;
 }
 }
 
 if (inAir && controller.velocity.y <= 0.0){
     if (fastfall)
     {
     gravity = 120.0;
     audio.Play();
     }
 
 }
 
 }
 
 function Gravity (){
 if (gravenabled)
 {
 moveDirection.y -= gravity * Time.deltaTime;
 }
 }
 
 function Update (){
 
 
 Jump();
 Move();
 
 if (controller.isGrounded)
 {
 jumpCount = 0;
 gravity = 35.0;
 airdash = false;
 gravenabled = true;
 airdashcount = 0;
 }
 
 Gravity();
 controller.Move(moveDirection * Time.deltaTime);
 
 }
 
 
 @script RequireComponent (CharacterController)
 @script RequireComponent(AudioSource)