onAfterElementSave and new elements
You should be using it like this:

public function onAfterElementSave()
{
    $fieldHandle = $this-&gt;model-&gt;handle;
    if ($this-&gt;element!==null) {
        $myData = $this-&gt;element-&gt;title; // just an example
        if ($this-&gt;element-&gt;$fieldHandle != $myData) {
            $this-&gt;element-&gt;getContent()-&gt;setAttribute($fieldHandle, $myData);
            craft()-&gt;elements-&gt;saveElement($this-&gt;element);
        }
    } 
}