weird loss of fps

just started today whether it be an online game or ut2004 which i play a lot my fps rate is way down. i checked all of my drivers and i have the latest of them. hard to explain but when something in game is supposed to be moving slow it really starts losing fps. as long as i keep moving at a fast pace every thing is fine. but if i stop and slowly look left, right or anywhere the fps go way down. also ive noticed in task manager. the cpu% usage steadily jumps from 2% to 10% rapidly while nothing is running, just sitting there idle. nothing is overheating and all voltages are good. any ideas.

• asus p4p800e deluxe
• p4 3.2ghz ht
• bfg 6800gt oc agp
• 2 gigs kingston ram pc3200 4 x 512
• ocz modstream 520w psu

edit... the cpu usage part i mentioned it doesnt show any processes using anything as it jumps from 5 to 10%, it shows it subtracted from system idle process but whats using it it doesnt seem to be showing. also forgot to mention i have scanned for viruses and spy ware and all was clean.

 

update....... i found my problem. after originally not being able to find the source of why i was losing fps and have eratic cpu% usage, i turned my pc off. when i came and turned it on a little while ago a norton anti-virus box came up and said it had detected (ibm00001.exe) and said it was a trojan of some sort and that it had been quarantined. so i rebooted and ran a virus scan just in case and nothing was found. the eratic cpu% usage is gone and the fps has returned to normal for everything. i dont understand why norton didnt find it when i ran the first virus scan when i was elimanating possible causes for the problems i was having. oh well im just glad all is back to normal.