How do I create unit test sequencing in vs2012?

I have some 200 unit tests for an app that run against a simulated piece of hardware with an asynchronous messaging api. All the tests run and pass individually but many of them will fail when run as a group, because of the asynchronous nature of the external calls.

Is there a way that I can set up test sequencing in vs 2012 so that I can add a small delay after each test to give the externals a chance to clear their cache?

edit: The order also seems to matter somewhat, certain tests lock up the external resources longer than others.