@n00bie:
You want to press the key once and speed "my" up to 3. And if you press it again it should slow down to 0 again?
Code:

---

var inc;
var status_accel = 0;

define speed, skill2;

function change_speed()
{
  status_accel = 0;
  wait(1);

  my = player;

  status_accel = 1;
  if(my.speed <= 0) { inc = 1; }
  else { inc = -1; }
  
  while(status_accel)
  {
    my.speed += 0.1 * inc * time_step;
    
    if(my.speed >= 3 || my.speed <= 0) 
    { 
      status_accel = 0;
    }
    
    wait(1);
  }
}

edit:
of course you need some entity pointer (like "player") to refer to it.

on_q = change_speed;

---