How do I add another field after saving entity metadata wrapper?
The problem can be with your field format. If your field other_field is a text field check what text format is set for it in admin/structure/types/manage/your_content_type/fields. EG:


If it is different from the plain text format you have to assign an array as a value to your field. EG:

$emw_node-&gt;other_field = array('value' =&gt; $id, 'format' =&gt; 'filtered_html');


or just  

$emw_node-&gt;other_field = array('value' =&gt; $id);