MGRV8 | Checking external air leaks into Plenum Chamber

Still pretty sure the misfire at tickover is related to an air leak into the intake manifold somewhere. To start off with I need to eliminate that an air leak may be originating from one of the units connected to the plenum chamber.

I disconnected each of the connections and sucked on the pipe leading to each unit to check that they can hold a vacuum. All were OK.