Updated 31st December 2013 based on personal testing, direct feedback as a result of this article and the conversation on the Intel Wireless Networking Community (67 pages about this problem so far …) here.
Purchasers of Laptops with Intel WiFi adapters seem to have been having a hard time of it lately and have been reporting one of more of the following issues:
On upgrading from Windows 8 to Windows 8.1, their WiFi no longer works or has become unreliable.
and/or
Even on Windows 8 (yet to upgrade to Windows 8.1) their WiFi connection is unreliable – or doesn’t work at all – see the protests at the Intel Support Community web site.
and/or
With Windows 8 or Windows 8.1, folk experience various application hangs or failures – like the new (to Windows 8) IE11 hangs or appears to mis-render pages and Lync and Outlook appear to hang or lose connectivity.
If you are experiencing any or all of these symptoms, do this:
a) It is generally held that the most stable Intel Centrino WiFi driver for Windows 8 is version 14.8.8.75. This is the base driver that comes in the box with Windows 8, so if you are still on Windows 8 (as opposed to 8.1) roll back your Intel WiFi driver to 14.8.8.75.
b) If that doesn’t work, or you are already on Windows 8.1:
1. Control Panel –> Programs and Features and REMOVE any Intel® PROSet/Wireless Software but DO NOT remove anything that says it is Intel® PROSet/Wireless Software for BLUETOOTH® technology
AND
2. UPDATE your Intel WiFi driver to 15.10.5.1 for Windows 8 or 15.10.5.1 for Windows 8.1.
IMPORTANT: ONLY install the updated drivers and NOT the full Intel® PROSet/Wireless Software – so only download and install the file that is:
Wireless_16.7.0_De164.exe for 64bit Windows 8.1
Wireless_16.7.0_De132.exe for 32bit Windows 8.1
Wireless_16.7.0_De64.exe for 64bit Windows 8
Wireless_16.7.0_De32.exe for 32bit Windows 8
[The “D” in the driver name, stands for “Drivers only” – and no, I haven’t the faintest idea why Intel should publish a driver update with a version of 16.7.0 which installs a driver version 15.10.5.1 …]
AND
3. Once the driver version 15.10.5.1 is installed and the PC has been re-booted, Control Panel –> Device Manager –> Intel(R) Centrino(R) Advanced-N 6235 –> Properties –> Power Management and REMOVE the tick from the “Allow the computer to turn off this device to save power” checkbox:
c) If you still experience problems once you have upgraded your WiFi drivers, then try the Intel WiDi Update Tool.
WiDi is Intel’s implementation of Miracast – which allows mobile PC screens to be 
projected wirelessly, via WiFi, to a suitably Miracast enabled display. Miracast requires the correct combination of Screen drivers, WiFi drivers and supporting software, so this is a good tool to run to ensure that you have all the correct drivers loaded for your particular laptop.
So, none of that worked?
OK, roll your sleeves up for this – but it’s not for the feint hearted:
Testing with friends and colleagues has now conclusively proved that some Broadband Routers with WiFi can hang and lose connectivity with Windows 8/8.1 devices if they have UPnP switched on (which is the default for most routers). To the laptop user, this router hang will appear as a local WiFi problem – i.e. the laptop user will think they have a problem with their Laptop Intel WiFi – when it is actually the router that you are connected to that has the problem.
Switching OFF UPnP on affected routers has a very high probability of fixing your WiFi network dropout/hang issue and to date, I haven’t found any adverse effects (Xbox gaming e.t.c. still seems to work fine with UPnP switched off).
Unfortunately, you will have to work out how to switch off UPnP for your particular router by reading its manual I am afraid, but I can tell you that testing so far indicates that the following routers hang with Windows 8/8.1 if UPnP is left turned on:
Plusnet, BE, Zen, Andrews and Arnold, O2,TalkTalk and other UK ISP’s Technicolor TG582N
Virgin Media (UK) Superhub
Orange/EE Broadband Brightbox (AKA the Arcadyan AR7516)
No, I have no idea what it is about Windows 8/8.1 which is causing a problem with UPnP in some routers – but I will update this article.
If you turn off UPnP on other routers and find that it improves stability, please tell me, and I can add them to the list here:
Windows 8 and Windows 8.1 WiFi works fine without having to turn UPnP off with:
Netgear DG834G V4 with V5.01.16 – DGTeam Rev. 1018 firmware
Windows 8 and Windows 8.1 WiFi works fine when UPnP is turned off with:
Technicolor TG582N – disable by clicking “Game & Application Sharing” in the toolbox menu and under “Universal Plug and Play” there should be a checkbox to enable/disable UPnP.
Virgin Media (UK) Superhub
Orange/EE Broadband Brightbox
–
Really useful stuff that I bump into..... 
thanks for the info, I made these changes but still had problems with my wifi.
i have narrowed it down to the hdmi connection – when i plug into hdmi monitor the download speed drops by 99%. my laptop is hdmi mini and i have convertor to normal hdmi cable. not found a solution yet but will update if i do.
Many thanks for this information. Turning off UPnP on my Orange Brightbox fixed the mysterious download interruptions on my new Windows 8 PC. It even caused downloads on other PCs connected to the router to fail.
Thanks aaa – great extra data that confirms the problem and associated fix – including that having UPnP turned on on this router impacts all devices on the network – not just the Windows 8 PC.
Note also: That if you have your router set so that the Wifi is 802.11N, then N WiFi does NOT support WEP encryption – you can only use WPA. HOWEVER, I think that some router manufacturers have configured their routers so that when presented with a WEP key over N WiFi, they automatically drop down to only transmit (and communicate on) 802.11G at 54Mbs and I think that in some instances, this switching could also be adding to the problem.
So the simple fix is:
– If you want to run an 802.11N network, all devices MUST use WPA encryption – and don’t mix N and G WiFi devices – make them ALL N.
– If you have some devices that can’t run N, you need to make ALL devices on the network run G.
Note also, that if you have a set of FitBit Aria WiFi bathroom scales – they only run 802.11B, so that might be an extra challenge. Just eat less doughnuts….
Woody.
Thanks, Woody, I don’t think I have any devices on the network using WEP.
It may also be worth noting that exactly the same problem occurred when I connected the Windows 8 PC directly via ethernet – it’s not just a wireless problem, at least not in my case.
Thanks aaa – and my apologies for not noticing your comment when first posted. It is particularly interesting, because Shaun has subsequently reported the same issue i.e. connected via ethernet, whereas all previous observations have been only on WiFi.
So great additional empirical data – thanks!
Woody.
Yes I have suffered with the Windows 8.1/Brightbox router problem for months now. As in some other posts my problem was with the Windows pc connneted via Ethernet and this interrupted internet connectivity to any other machine hanging off the router regardless if it was WiFi or cable connected. Other devices seemed to connect better when the pc was turned off. I’ll try the disable upnp fix tonight.
Shaun,
A big thanks for this – please do report back if this works for you – as I have had two additional reports privately (from Brightbox users) yesterday, that turning off UPnP has for the first time allowed them to have > 75min uninterrupted Lync calls (VOIP) – which was previously unheard of (if you’ll pardon my little pun).
Thanks,
Woody.
Well Woody after months of tearing my hair out…(and I don’t have much left to start with), turning the UPnP off on the Brightbox seems to have sorted it. No more mysterious download hangs, my cloud printer stays online and streaming to WiFi connected devices works every time.
Not sure if this is related but looking in the log in the router settings I used to get a lot of DOS (denial of service) attacks by the Windows 8.1 computer (internal IP address). I’ve not spotted it since but I will keep an eye out to see if turning off upnp has stopped the alleged attacks.
Thanks for the tip.
Cheers
Shaun
Shaun,
LOL – I am glad this worked for you – as in a twist of fate, my trusty Netgear failed and EE have just sent me – yes, you guessed it – my very own Brightbox!
Thanks so much for taking the time to confirm this fix works for you.
Woody.
Im having this issue with my home wifi, all my devices work fine with it but my laptop with ac 3160 connects to 1mbps when im 12 ft away, wich is stupid, do you think changing the UPnP is the issue even if the other devices are working? The first solution didnt work, but thanks anyway! Im having the hardest time with this laptop, is the first thing I bought with my first salary and im regreting ti big time!
Penny your laptop should connect to your router fine over WiFi, but you will only get the added advantage/speed from the AC3160 in your laptop if your router/WiFi Access Point is also “AC”.
There are some more fundamental things that may be giving you this problem (of which UPnP may be one) but I can’t help unless I know precisely what model your router (and home WiFi point – if different) is.
Thanks,
Woody.