Determine which application pool's worker process (
w3wp.exe) is hogging your CPU resources. The command below can be run in a command prompt to list IIS Application Pool PID's. To view process ID's in task manager navigate to View | Select Columns | PID.
I've needed to do this several times when a single worker process was consuming too much cpu resources and needed to be killed. Stopping the application pool did not help.
%windir%/system32/inetsrv/appcmd list wp