ok, then which processes are you talking about? Plesk launches backend utilities (websrvmng.exe, ftpmng.exe, dnsmng.exe, ...) to perform configuration of system (IIS, MSDNS, etc). These processes work for some limited time, and it is OK if in some cases they consume 100% of CPU for a limited time.
Can you provide examples of processes that you "shut down manually"? And how long these processes are working before you shutting them down?