The dirt / grime that dry ice blasting process removes has to go somewhere and likely would get thrown around the engine bay. There's a reason the people that do it on undercarriages wear suits; so they don't get covered in all that crap. I wouldn't think that's worth the effort and cost to attempt on installed engine parts. Also, it wouldn't be able to reach the back and underside of the plenum for a full cleaning. I'm all for dry ice. I just don't think this is the right application.
