Menu problem

1

Im trying make a menu type thing that scrolls in and out on a user click however it just goes nuts I just need a couple of tips on how to get it to work.

 
on(press){
 onEnterFrame=function(){
 
  if(_root.menu._x <90){
  _root.menu._x+=3;
  trace(_root.menu._x);
  }else if(_root.menu._x >90){
  _root.menu._x-=3;
  trace(_root.menu._x);
  }
 }
}

this code means that when it gets to the end it just starts jumping back and forth could some one please just help a little!

many thanks