Does OEMIdle will affect the speed of usb data transmission?

I implemented the OEMIdle funtion on S3C2440 CPU with PB5. The power was
saved evidently, but when I used the devce as a USB Mass Storage through USB
Slave port, I found the transmission speed was very low, and the whole
process proceeded off and on.

Is there anything should I pay more attention about the S3C2440 on OEMIdle?

Any suggestion will be appreciated. Thanks!