on an M117 it should be seated shut (Actually there is a small amount of air that still bleeds thru by design) @ 66 Celsius not 80.
Clean by spraying with a quality parts wash (Repco) or Repco brand degreaser and watch the amount of carbon flushed out, leave to soak overnight in the solvent cleaner and blow out again with the pressure pacK degreaser (Repco again).
Do this until you no longer flush out black carbon and rinse using brake cleaner which leaves zero residue (Repco brand again)
So.... Flush and flush again, soak overnight and flush again, soak over night and flush with brake cleaner as a final rinse.
Test unit before and after with hot water and a thermometer ($5 meat thermometer is fine) and the unit should shut at 66 centigrade.
I thought it was 80 but the Bosch spec is 66 Celsius.
BTW, is your M117 (450/380) a D jet or K jet engine?
Tony