[Halon]

If your FIAV is working properly, blocking it off should really only affect it when your motor is cold, like when you first start up your car in the morning. That's all it really does is let some extra air by when the motor is still cold. So if you block it off, it wouldn't let any air by when the motors cold, so it would idle a little more rough, when the motors cold.

But if you didn't actually use a block off plate, and you left it in there and just stopped running coolant to it, well then it would be constantly letting air by, so your idle would probably actually be higher.