1981 380 SLC Runs at high Idle. IAC does not change/compensate for driving speed/condition. I replaced seneral used known good IAC's but idle changes to last setting on IAC and vehicle does not have power with key "ON' car "OFF".
Someone had put small pieces of vacuum line in the IAC port to restrict the flow od air and possible manipulate the setting.
This is an 1981 380 SLC, you don't show one in your options only SL.