G'Day,
If the BOV is venting at idle it is either stuck/faulty or hooked up incorrectly, from what you have said it is std ECU? How did you do that? Dumping more fuel in will NOT open BOV at idle.
Make sure all your Vac/Boost lines are hooked up correctly, if it is running REALLY rich with no EWL on, check your vac readings at idle, if your BOV is open at idle, it will be sucking air, resulting in a lean idle, which the ECU will add extra fuel to compensate the lean mix, resulting in an increase of idle speed. Not a whole lot of info to go on.....
But I hope this helps somewhat....
Cheers
Sixpack Subaru