Q:

Windows XP Task manager system idle is at 98% but graph shows one processor nearly pegged

Running Windows XP on a AMD dual core processor.   Occasionally after booting, logging on, and letting things settle down, the Task Manager shows on the graph that one processor is over 90% busy.  Yet when one looks at processes running, system idle is at running around 98%.   On performance graphs, the CPU usage bar shows as red with tiny amount of green.  Only one user is logged on.
It is as though there is a rogue task that task manager doesn't know about when showing the processes, but does know about when showing the performance graphs.   
I have seen this several times.   What I've done in the past is reboot the system, and the problem/anomaly was no longer present.  A log-off / log-on did not get rid of the rogue usage.
I have not explored if the issue is triggered by a long delay from power-up to log-on.
System seems clean on anti-virus scans.  Network activity is zero.  
Any ideas as to what might be happening?

A:

I'd try googling for the sysinternals suite and run process explorer to see if that can give more information on what is running on the processors.
Failing that you can also run process monitor and that will tell you what processes are issuing file and registry I/O and see if something there is constantly busy (use the autoscroll option from the menus to see real-time changes).

