[Tweener] Adding tween

[Adrien]

Hello I'm trying to add a tween to this

import caurina.transitions.Tweener;

function moveClip(p_clip:MovieClip, p_dir:String,  
p_distance:Number):Void {
   p_clip.count = 0;
     p_clip.onEnterFrame = function() {
        p_clip.count++;
           if (p_dir == "up") {
                this._y -= 1;
            }else {
               this._y += 1;
            }

         if (this.count == p_distance) {
            trace(this)
            delete this.onEnterFrame;
         }
     }
}


I've tried this but doesn't work... do you know what I'm doing wrong?  
it has something to do with the minus and plus but why?

import caurina.transitions.Tweener;

function moveClip(p_clip:MovieClip, p_dir:String,  
p_distance:Number):Void {
   p_clip.count = 0;
     p_clip.onEnterFrame = function() {
        p_clip.count++;
           if (p_dir == "up") {
                Tweener.addTween(this,{_y -:1, time:1});
            }else {
               Tweener.addTween(this,{_y +:1, time:1});
            }

         if (this.count == p_distance) {
            trace(this)
            delete this.onEnterFrame;
         }
     }
}

Regards
Adrien