DFU Loop

A DFU loop only happens when you've put your iPhone into True hHardware DFU Mode. Sometimes during the restore with your messed-up IPSW, iTunes will error out with an Error 31. This indicates that your device is in True Hardware DFU Mode. This mode can't be exited. You're in a DFU loop. Any time you try to reboot the device, it goes right back into DFU mode. Only solution is to restore a working IPSW.