BigJim (if that really is your name)
I don't have a lot of experience with unbound sub forms, however you might try to put the name of your combo box in the criteria line of the matching field of the Query. Say your sub form displayed employee information. The Query might be selecting fields like emp_no, emp_name, emp_address etc. The Combo box on your form would have a SELECT query as it's recordsource that Selected emp_nos and Emp_names but only displayed the names. In the emp_no field of the query you would have a criteria of ...
=[Forms]![FormName]![ComboBoxName]
Then you go ahead with the call to requery or refresh the subform (either should work). Thereby the Query is called using the current value of the Combo Box.
I think that should work
Chris