Trigger scriptaculous ajax autocompleter in the update function

Question

I'm trying to create something a text input field where you can enter a kind of path. I try to help the user with autocompletion, so that he may click trough the path instead of writing it down. It works almost, but there is one little problem left. With this code:

memoFolderAutoCompleter = new Ajax.Autocompleter('folderPath', 'selectorField', 'folders.vm', 
  {
 afterUpdateElement:function (text, li) {
  text.value +="/";
  memoFolderAutoCompleter.onObserverEvent();
 }
});

I am able to trigger the autocompletion right after selecting a path so that the next level down in the path would be selectable. The Problem is now, that the field with the choices is not shown without any further input. By pressing for example the down button it shows up and it already contains the right choices without a new ajax request. But i would like to see the choices instantly.

Does anyone know how to do that? Thanks raffael