October 28th update: after speaking with our contact at the local Toyota dealership, not much is known about this issue beyond Toyota looking for any Prii with said codes that are easily reproduced. This leads us to believe Toyota is putting together a fix for the issue. We’ll do a complete posting on whatever fix become available as it becomes available.
Toyota just released T-TT-0310-14, a notice to technicians to stop any diagnosis of Prius misfire rattles with a P0301,P0302, P0303 or P0304 and contact Technician Assistance before going any futher.
As such, CARspec no longer recommends intake manifold replacement as a potential repair and is awaiting the final verdict from our sources at the dealership regarding the issue.