How to enable iframe code for the TinyMCE Editor

For enable Iframe code for the Tiny MCE Editor, Go to Extensions -> Plugin Manager -> Editor – TinyMCE(you may search it using keyword 'TinyMCE' in Plugin page). Open it, than find "Prohibited Elements" area.

Now you can remove "iframe" tag from this list of prohibited elements. At the end be sure to save your changes when you're done.