While it is operational, do some of the tests suggested to see if the cylinder(s) giving trouble can be identified. I don't think the ICM's would have any features removed. Why they don't work is unclear, but while it is operational, check the things that you can. Then perhaps swap in one part at a time if desired. Just go through diagnostics and write down each reading as you step through the ECM data while it is idling. Maybe something will jump out??
Make doubly certain the spark plug connections are in the correct order. It is very easy to switch two of them on the rear bank. It has caught out many before you.