[dBlast]

TPS senses throttle position in the TB.

IAC sensor is further down in the manifold. It senses idle air?

If you look at your FC TB closely there are 3 tiny holes on the side that bypass the butterfly valve. This allows air to flow to keep your engine going at idle even when the butterfly is completely closed. If you have the original gasket there are holes to allow this air to pass. Perhaps on the new intake there may be a blockage, or if you changed or made your own gasket there may not be enough air bypassing to reach the IAC sensor.