IDLEDISABLE prevents the CPU from throttling itself, causing heat and the fan noise I observed. Additionally, this manifested in the Task Manager as “100% CPU usage”. Process Explorer seems to always discount the System Idle Process and not include it in the total CPU usage, which is why it displayed a lower total CPU usage than Task Manager did.
To fix this, you can run the following two commands, which sets the IDLEDISABLE setting back to “0” and then re-applies the power management configuration.
C:\WINDOWS\system32>PowerCfg /SETACVALUEINDEX SCHEME_CURRENT SUB_PROCESSOR IDLEDISABLE 000
C:\WINDOWS\system32>PowerCfg /SETACTIVE SCHEME_CURRENT