char speed need help

I new at c# scripting and I trying to make character change speed here is the script below: [code]

  if (Input.GetKeyDown("w")) {
         if (_Speed == 0) {
             _Status = "Please increase speed first";
         } 
         if (_Speed == 0.3f && stoping == false){
             
             _ChargeTime -= Time.deltaTime / 10;
             Debug.Log (_ChargeTime);
             _Status = "Charging.." + _ChargeTime;
             _fakeSpeed = _fakeSpeed - 0.1f;

             if (_ChargeTime <= 0) {
                 _ChargeTime = .5f;
                 _fakeSpeed = 3f;
                 _maxSpeed = 3f;
                 _RotationSpeed = 0.01f;
             }
         }
     }

[/code] so what I want to do when I press W key speed decrease (-0.1f) then timer count few mili seconds and then full speed. but something wrong here timer starts counting and stops at 0.4983433. i think because I set up _fakeSpeed = _fakeSpeed - 0.1f but not sure. any help? :)