Fan speed decreases, with more CPU temperature?

[Emer1ca]

Hi my CPU FAN decrease from 1400 RPM to 700 - 800 RPM when i play games like Battlefield 3.

My normal CPU temperature is 28 - 35 ºc at 1350 RPM, and when i play games like BF3 the temperature go to 75 - 80 - 90 ºc and the CPU FAN RPM decrease to 700 - 800, i and dont know why, please help me thanks.
My PC
-Gigabyte GA-H57M
-CPU Intel core i5 760
-GPU Nvidia Geforce GTS 250
-power supply Corsair 550wts

 

[WR2]

That's not good.

You didn't list the CPU cooler make/model.
Also, what case and case cooling do you have?

 

[suteck]

I would go into bios ( or whatever program you have running the fan speeds) and turn off the fan modulation and let it run full out and see how that works.