When hot:
Car was fine with old ICV, not fine with new ICV.
Disconnecting new ICV makes car run better?

Hmm, taken in isolation that points to a duff/incorrect sensor imho.
I have no cossie or electronics experience, just going by what you've said.

Of course I'm conveniently ignoring the cold-start problem - but this could be a different issue with a different cause, given the new sensor failed to address it.