RedSn0w 0.9.6 RC9 is already been released by iPhone Dev team for untetethered jailbreak on iOS 4.3.1 devices. Except iPad2, all other idevices can be jailbroken with this update of RedSn0w.
You might be looking guides for this jailbreak. Here, we are presenting a video guide from blogsdna for the jailbreaking so that you do not find any difficulty in the process.
Video of Untethered Jailbreak 4.3.1 with Redsn0w 0.9.6 rc9 Video