My MacBook Air has recently started having substantial WiFi connectivity issues. How do I fix this?

Question

For the last couple weeks my MacBook Air has started having some mighty substantial connectivity issues.
When I wake it from sleep, or if I'm using it for an extended period (say, more than 5-10 minutes), the connection will become extremely unreliable. This primarily happens with browsers, or the Twitter application. For example, if I start a call on Skype the call will continue to function just fine, but I won't be able to connect to any websites through any browser. I've tried Safari, Chrome, and Firefox while the connectivity problems are occuring. When they do occur, a full shut down and cold boot are required to make it work again for a short while.
Does anyone know what might be causing this? I've done numerous checks for malware using Clam Xav and Sophos Anti-Virus. (I didn't suspect that this would be the issue, but it was still something that I decided to rule out.) Additionally, I've tried connecting using both the 2.4GHz and 5GHz bands on my wireless router. Neither seems to be more successful than the other. (Note: The 5GHz works perfectly and without interruption on my iPad and desktop PC. The 2.4GHz works perfectly with my iPhone 4S and Xbox 360. I feel that with that in mind, I can safely rule out the router as the root of the problem. Both of these examples go on for very extended periods of time. I game regularly using both my PC and Xbox 360.)

Answer 1

Hi Jollified,
Does your sound work when you try to use head/earphones? If so, try the following:
Plug your Headphones into your Mac.
Play a sound through them (a song for example), then stop the sound.
Make sure 'Preferences' is isn't open. If it is, Quit.
Launch System Preferences > Sounds.
While the Sounds tab is open and set to 'Headphones', pull out the Headphones from the jack.
You should see your Mac reset to 'Internal Speakers'
Also, I see you have tried resetting the PRAM, have you tried resetting the System Management Controller (SMC)? Resetting the System Management Controller (SMC) on your Mac - Apple Support
As for your MacBook not sleeping when you close the lid, there are many reasons this can occur.
First of all, check out Apples article on the issue: OS X Yosemite: If your Mac won’t go to or stay in sleep If you find these steps don't help, try a few of the following:
A common cause for the Mac not sleeping is your printer. If there are queued jobs waiting to be printed, but your printer is switched off, for some reason you Mac just wont like it and simply will not go to sleep. System Preferences > Print and Scan > Open Print Queue
Do you have an Ethernet Cable connected? People have reported in the past that removing their Ethernet allowed their Mac to sleep. This goes for other things you may have connected directly to your Mac also.
Try heading into your Mac Preferences > Sharing and deselecting 'Internet Sharing' as well as 'Printer Sharing'.
Also deselect Wake For Network Access by heading to System Preferences > Energy Saver > Power Adapter > Wake For Network Access.
Energy Saver > Schedule > Startup or Wake - Uncheck.
Alternatively, set your system preferences to Never Sleep, and put into Sleep manually: System Preferences > Energy Saver > Computer Sleep > Never.
Good luck!