Q: Wifi is incredibly slow on OS X El Capitan

I also experienced this problem usually when I am far from the wifi router. The way I have come around it is by switching off the iPhone's wifi. It appears to be some type of wireless interference with the iPhone and Macbook wifi, both become extremely slow or stop working.

Not sure if this is a problem of El Capitan or iOS 9.0.2, but I have been experiencing these problems ever since I updated both OS.

Well, I think I sorted my WIFI issues!!

Just so you know how I have my Mac set up here.

I have 2 LG monitors connected to my MacBook Pro Retina mid 2012 via the 2 thunderbolt ports.

Mac is (usually) with closed lid and power connected. Always worked like this and never had a problem.

Now, after El Capitan, with the set up above, my WIFI was dead! The exclamation mark was showing on the top bar.

I decided to connect to the internet by plugging the ethernet cable straight instead of using WIFI, so I unplugged the 2 monitors, opened the lid and before connecting the ethernet cable I ran a speed test.

For my surprise, the internet was connected and running super fast as usual!

Ok, I thought the 2 thunderbolt monitors were somehow killing the WIFI.  I connected 1 monitor only, closed the lid and ran the test. WIFI problems again. Plugged the 2nd monitor, ran test, still very very slow.

Kept the 2 monitors connected, opened the lid, ran the test and VOILA! WIFI is back again! Super fast and stable!

So I closed the lid again, ran the test, boom, internet speed dropped! I did this many times and experienced the same thing.

I can't believe that having the lid closed on my MBP is the real issue, but so far this is the best test I could do and see that somehow I managed to get my WIFI back by keeping the lid opened.

Again, I will keep testing this so please let me know how it goes your side. I will shoot a video tomorrow to show this happening.

When I check my WiFi speed after my MacBook sleeps, it's slower by half.  If I restart the 12" MacBook, the speed returns to normal.  An El Capitan issue?

Hi grahammiranda

I'm having problems with WIFI in Yosemite, sometimes it get slow suddendly and stays that way until I reboot on "safe mode", this is very easy but  a bit slow.

I would encourage you to do this simple test:

1- first, run the speed test of Ookla: http://www.speedtest.net/es/

2-reboot while pressing "left shift" key until you see your user (then login it), your desktop (it will run very slow and with some graphical glitches)

3-once in your user  just reboot again (normal)

4- run the Ookla test again

hope it helps

I was looking around for solutions after noticing my retina macbook pro late 2013 was only getting 80 Mbs download speeds on a/c while my ethernet connected mac mini was getting 340 mbs download.  The wireless a/c at 5 ghz should be capable of higher than 80.  I tried resetting the PRAM and on my first speed test using OOKLA shortly after restarting I got 340 MBS download on my wireless....then the test failed with a "socket error"  and then subsequent tests have all been back to 80 mbs down/ 20 up.  Resetting PRAM again didn't get me above 80.  I guess I should count my blessings but from everything I've read my wireless should be capable of more than 80 (I live in an isolated area, no wireless congestion) when my ethernet is getting 340 down !

I was actually wondering if it's some function of the plugin for Ookla speediest or my Sophos that's running in background?  Would appreciate any thoughts.

on a whim i plugged my macbook pro into power, closed and reopened Safari, and tried again and now I'm getting 340- 350 mbs download speeds !  I wonder if it's a power saver issue of some kind limiting download speeds when on battery??

I'm having this issue as well. My 100mbps wifi connection at work now only gets around 1.2mbps after upgrading my 2012 Retina Macbook Pro to El Capitan. My desktop iMac still running Yosemite is still running at full speed so I know it's not the network.

I've tried resetting the PRAM, renewing the DHCP, and resetting just about everything else I've read about on this thread with no luck.

Interestingly, I have noticed that the problem doesn't exist when I am on wireless networks using Apple routers. My home connection has a first gen Time Capsule router & performance is normal.

Really hoping Apple takes this seriously and addresses it soon. I have to work remotely for the next few weeks.

There's clearly something wrong in the WiFi driver and/or the software that picks up the installed devices at boot time. 

I am using an Apple Airport Express in my hotel room.  The hotel wired connection yields ~84Mb/sec download and upload.  The hotel WiFi was both unreliable and poorly performing for all of my devices (MacBook Pro Retina running El-Capitan, iPhone 6  Plus and iPad Air 2).  I then shared my MacBook Pro wired connection via WiFi and got good performance on my iPhone and iPad.  But I didn't want to be tethered to the wall, so I got the Airport Express.  Now my iPhone and iPad get near the ethernet rate when using the Airport Express, i.e. ~70Mb/sec to 80Mb/sec.  The Mac Book gets ~1Mb/sec!!!  The stack above the driver (IP etc.) is the same for wired and wi-fi. I'm using the same application to test speed.

Now I noted an earlier comment with regards to monitor interaction...  When I upgraded to El-Capitan, my monitor behavior when I connect my MacBook to my 2 monitors (Thunderbolt display and Samsung 4K display) is completely random, in terms of El-Capitan picking up the displays (sometimes it fails) and their resolution.  The Thunderbolt display often ends up with the wrong resolution.

Is there something wrong with the way El-Capitan scans for devices and configures its drivers at boot time?...

I was having WiFi issues as well with the new el capitan.  It would drop out and then be ok then run slow.  I performed the procedures on this link and it works great now.

http://osxdaily.com/2015/10/16/fix-wi-fi-problems-mac-os-x-el-capitan/

- Wi-Fi takes a long time to connect after sleep or startup for known access points. This was never an issue with Mavericks.

- Sometimes will not connect at all. Have to cycle Wi-Fi off and on again.

- Wi-Fi will stop working, no data being received despite being connected to an access point. Have to cycle Wi-Fi off and on again. Happens randomly.

- Wi-Fi speeds are incredibly slow. Speed test on MacBook and iPhone 6s next to each other reveal vastly differing results. iPhone: 68Mbps. OSX: 24Mbps. (Did not run these tests at the same time).

I updated my computer and thought there was a bug with the update so I did a clean install, still experiencing the same issues on a fresh install.

Actually El Capitan had nothing to do with the issue.  I realized that I had so many wifi devices on auto that conflicts were created.  I just changed most of the devices to a static IP with their own address and the issue was resolved.

You and probably few people on this forum will want to hear what the fix for this is.....  Its called Windows 10. 

I bought a $300 Asus netbook with Atom processor and upgraded it to Windows 10 for my 12yr old son.  That thing is so fast and reliable and has a fraction of the processor and storage that my Macs have its incredible.  El Capitan killed my Mac Mini Late 2010 (8Gb with 1TB HDD) with and there are good and bad days on Macbook Air 2010.  Wifi on the Air has been an on and off issue since Lion.  I'm too scared to upgrade my Mac Mini Server.

iOS 9 gave my iPhone 5 the black screen bug when opening apps even native iOS apps like Settings.  iOS 9 made my iPad2 very very slow.  The Windows 10 Atom kills it in every respect far more pleasant to use.

To be fair, its very kind indeed of Apple to offer free upgrades but the upgrades should be optional and not of beta quality.  I say they aren't optional because about this time every year, whether by "design" or "accident" the performance of my apple products suffer noticeably leaving upgrade the only realistic option.

But I'm off to the shop tomorrow to buy another Atom Netbook.  Windows 10 is the fix.  BTW the user interface is a gem.  The only complaint is inability to set scrolling to "natural".

OK, so that was helpful... Not.  This is for people trying to get help w/ Apple products, if you've got nothing to add except 'switch to windows' -- call us when you're wracked w/ spyware and viruses and your crappy $300 netbook is slow in 6 months.  This forum is user to user help -- and you're not helping at all.

At some point I was thinking it was El Capitan causing the problem. This slow wifi problem started a few days ago after upgrading to El Capitan.  I did all kinds of tricks to fix the slow wifi. However I noticed wifi in a Macmini with Mavericks was also slow.  I activated the 5GHz option in my Airport Extreme and now all    devices connect easily and have a fast wifi. You need to select the 5GHz network.