My 2006 Lexus gs300 throws a code p0505 idle air control system

No you will not screw the computer up. You can replace it yourself but try leaving the battery disconnected while you do it to reset adaptations. Worst case adaptations will need to be reset with a professional scan tool. Alex

I highly recommend a second option here! .. Suggest contacting local auto repair facility and make arrangements for testing. Reason is this is an unusual problem for that vehicle.. Thus may be corrected by simple adjusting base idle and performing idle re-learn procedure. Good luck With It!