Earlier today Apple released iOS 4.3 for iPhone 4, 3GS, iPad, iPod touch 4G, 3G and Apple TV. So if you are one of them who upgraded to iOS4.3 , and now want to downgrade back to iOS 4.2.1 or 4.1. So here are the instructions posted below to downgrade iOS 4.3 on iPhone 4, 3GS, iPod touch and iPad to iOS 4.2.1, 4.1, 4.0.x.
Note: This guide is only for those who saved SHSH blobs for the respective firmware you downgrading to.
Step 1: Download the required old IPSW firmware files. (Download)
Step 2: Put your device into DFU mode and run iReb on it in order to Avoid Any 16xx Error.
Note: Your iPhone, iPad or iPod touch screen at this time should be blank (black in color), if not, then you are most likely in Recovery Mode, not DFU mode.
Step 3: Now run iTunes,From the iTunes sidebar select your device. Now press the “alt” (option) button on Mac or left “Shift” button if you are on Win and then click on “Restore” button in the iTunes.
This will make iTunes prompt you to select the location for your iOS 4.2.1 or 4.1 firmware file. Select the desired IPSW file and click on “Open” to restore your iOS device.
Now relax and let iTunes to restore iOS 4.2.1 for your iPhone/iPad/iPod Touch. During the restore process iTunes may throw some error message (Like 1015), and you will be in Recovery Mode. Just ignore this error.
To by pass this error follow the Steps Below:
Download these files to fix Recovery Boot loop on iOS4.2.1 and iOS4.3.
For MAC OSX
When you downloaded the above files so put them on the Desktop.
When you open it and gives a error like Zilb1.dll not found, So download the Zlib1.dll from here and put it in C:/Windows/System32. (At first it gave me the error download the file only if it gives you or else don’t).
Put your iDevice into DFU Mode. Once in DFU mode it will show like this:
A new CMD Like window will open an Process will start like this:
When it will be done, the windows will close and some process will start on you iDevice. Don’t worry that’s normal. When you will done your iDevice will boot and in no time you will have the Activation Screen.Then Finally you will be done.
The procedure for iOS4.3.1 and above will be the same, So follow this guide every time you need to Downgrade.