How to restore your iPod/iPhone/iPad to iOS 4.2.1 from 4.3
If you are like me, you immediately upgraded your iDevice to 4.3 when it was available. Now you are probably thinking, you miss your untethered jailbreak and can’t wait for a new one, or you are being driven insane with the iPod pixel glitches (That annoys me the most!). The solution is to downgrade back to our trusted 4.2.1 (or any other firmware)! Now, you will need your SHSH blobs saved in Cydia for the firmware version you want to downgrade to. I decided to downgrade to iOS 4.2.1. A warning though, if you want to restore to backup, you will need to have one for the firmware version you downgrade to. Sadly I didn’t know this and saved a backup for 4.3, but after restoring, iTunes told me I couldn’t restore the backup because I have older software 😦 Make sure you also know the location of your firmware file (you can find download links on google).
Put your iDevice into DFU mode, you can do this by turning your device off (with it plugged in already) and holding the power for 3 seconds, then hold the power and home button for 10 seconds (your screen will go black with no text or anything on it sometime during this step) then hold only the home button for 15 seconds (or until iTunes gives you a message saying that it has found a device in recovery mode)
(Make sure iTunes is closed now) We need to change your hosts file, you will need an Administrator account (I don’t have a Mac, so I can’t give you instructions on how to do this, but Google is your best friend!) . Open your start menu and go to All Programs > Accessories > Notepad (On Vista / Windows 7, Right click the program and Run As Administrator) and go to File > Open and go to My Computer, then go to the C:\Windows\System32\drivers\etc and under the file type (Where it says “Text Documents”) change it to “All Files”, you should then see a file called hosts, open it and insert this line at the bottom
Then go to File > Save
Open back up iTunes and click on your iPod on the left side under “Devices” and hold down Shift and click “Restore” (on Mac you hold down the Option key), iTunes will ask you where your firmware file is. iTunes will then start restoring your iPod as normal, if you don’t have your SHSH blobs saved in Cydia (on Cydia at the top of the homepage it would say “SHSH: iOS <insert firmware version here>”) you will get an error from iTunes. At this point you should be done except for one more thing, when your iPod is done restoring make sure you take out that line of code we put in the hosts file (follow the step 2 only remove that line that I told you to put in instead of putting it in).
That’s it! See you later!