What was found
During descent on Flight #3531, #3 Engine was in a sub-idle Power setting into DTW. 15% N1, 45% N2, Oil Pressure 35 PSI, after Landing EGT started to climb past 560. Crew shutdown Engine.Maintenance replaced #3 Engine ECU IAW RJ85 AMM Ch73-20. PN 2-303-493-06, SN OALG815.