Byzantium

I had the same problem. I believe he is talking about system.exe not idle system. From reading other forums I found many different causes the most obvious was worms or Trojans but on clean machines this was still occurring on win2k and winXP machines. The cause I think applies here is spybot S&D. If you have block known bad sites checked it fills the HOSTS file with extra 127. entries. Over time this massively lags the system and leads to the system.exe using 90+% of your cpu. For me it was a local printer that had run out of ink. I turned it off and watched my CPU usage drop from 99 to 0. That was a beautiful thing I assure you. Other causes ranges from jumper setting on HD's if you have multiple HD's, needing to disable NetBIOS in TCP/IP, and even antivirus checking emails with a firewall set. Each of these things only shows up as system.exe eating 90+ of your cpu. None of the other process or running programs appear to be taking any more than normal resources.