Hi Paul,
Did you get a fix to this.
I went to another garage today as their Snappy scanner would not communicate with it.
This one would run for aprox 15 - 20 mins then shut down.
Only code was IAT signal too low.
I found the same IAT, CTS & idle speed as you.
Also the map sensor reading at 255Kpa.
Map reading would not alter even when engine speed increased.
IAT sensor removed, cleaned of gunge and refitted with no change to readings, New sensor fitted, also with no change to readings.

Even with the combined IAT/map/boost sensor plug and the CTS plug disconnected, readings still showed CT 215, IAT 215 deg and Map 255Kpa.

I did find a dirty earth connection on N/S inner wing, so cleaned & reconnected.
Spoke to garage owner after I left and he said the car ran for over an hour without shutting down.
Wondering what your fix was .. if any??