Wifi on iMac slower than other devices

Thanks Old Toad and iCare. I followed the instructions in the link your provided, iCare, but the problem persists. Here's the results from EtreCheck...

EtreCheck version: 4.3.6 (4D041)

Report generated: 2018-09-21 10:13:14

Download EtreCheck from https://etrecheck.com

Runtime: 2:01

Performance: Excellent

Problem: Other problem

Description:

Internet speed is slow both on WiFi and Ethernet connections

Major Issues: None

Minor Issues:

These issues do not need immediate attention but they may indicate future problems.

Clean up - There are orphan files that could be removed.

Unsigned files - There are unsigned software file installed. They appear to be legitimate but should be reviewed.

System modifications - There are a large number of system modifications running in the background.

32-bit Apps - This machine has 32-bits apps that may have problems in the future.

Abnormal shutdown - Your machine shut down abnormally.

Hardware Information:

iMac (Retina 5K, 27-inch, Late 2014)

iMac Model: iMac15,1

1 4 GHz Intel Core i7 (i7-4790K) CPU: 4-core

32 GB RAM - At maximum

BANK 0/DIMM0 - 8 GB DDR3 1600 ok

BANK 1/DIMM0 - 8 GB DDR3 1600 ok

BANK 0/DIMM1 - 8 GB DDR3 1600 ok

BANK 1/DIMM1 - 8 GB DDR3 1600 ok

Video Information:

AMD Radeon R9 M295X - VRAM: 4096 MB

iMac 5120 x 2880

Drives:

disk0 - APPLE SSD SM0256F 251.00 GB (Solid State - TRIM: Yes)

Internal PCI 5.0 GT/s x2 Serial ATA

disk0s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk0s2 [Core Storage Container] 250.14 GB

disk1 - Macintosh HD (Journaled HFS+) 249.82 GB

disk0s3 - Recovery HD (Journaled HFS+) [Recovery] 650 MB

disk2 - Western Digital My Passport 25E2 4.00 TB

External USB 5 Gbit/s

disk2s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk2s2 - A********U (ExFAT) 4.00 TB

disk3 - Western Digital My Passport 0748 1.00 TB

External USB 5 Gbit/s

disk3s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk3s2 - T**********e (Journaled HFS+) 999.83 GB

disk4 - Western Digital My Passport 25E2 3.00 TB

External USB 5 Gbit/s

disk4s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk4s2 - R*****s (Journaled HFS+) 3.00 TB

Mounted Volumes:

disk1 - Macintosh HD 249.82 GB (64.32 GB free)

Journaled HFS+

Mount point: /

disk2s2 - A********U 4.00 TB (2.59 TB free)

ExFAT

Mount point: /Volumes/A********U

disk4s2 - R*****s 3.00 TB (895.09 GB free)

Journaled HFS+

Mount point: /Volumes/R*****s

Network:

Interface en0: Ethernet

Interface en4: Thunderbolt Ethernet Slot 1

Interface fw0: Thunderbolt FireWire

Interface en1: Wi-Fi

802.11 a/b/g/n/ac

One IPv4 address

4 IPv6 addresses

Interface bridge0: Thunderbolt Bridge

System Software:

macOS Sierra 10.12.6 (16G1510)

Time since boot: Less than an hour

System Load: 1.26 (1 min ago) 1.98 (5 min ago) 1.80 (15 min ago)

Security:

Unsigned Files:

Launchd: /Library/LaunchDaemons/com.nvidia.cudad.plist

Executable: /Library/Frameworks/CUDA.framework/Versions/A/Resources/cudad

Details: Exact match found in the whitelist - probably OK

Launchd: ~/Library/LaunchAgents/com.akamai.single-user-client.plist

Executable: ~/Applications/Akamai/netsession_mac

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchDaemons/com.adobe.fpsaud.plist

Executable: /Library/Application Support/Adobe/Flash Player Install Manager/fpsaud

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchDaemons/com.wdc.WDPrivilegedHelper.plist

Executable: /Library/PrivilegedHelperTools/com.wdc.WDPrivilegedHelper

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchDaemons/com.microsoft.office.licensing.helper.plist

Executable: /Library/PrivilegedHelperTools/com.microsoft.office.licensing.helper

Details: Exact match found in the whitelist - probably OK

Launchd: ~/Library/LaunchAgents/com.redgiantsoftware.updater.plist

Executable: -a '/Applications/Red Giant Link.app' --args --silent

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchDaemons/com.nvidia.cuda.launcher.plist

Executable: /Library/PreferencePanes/CUDA Preferences.prefPane/Contents/Resources/CUDAd.sh start

Details: Exact match found in the whitelist - probably OK

32-bit Applications:

91 32-bit apps

Kernel Extensions:

/Library/Extensions

[Loaded] CUDA.kext (NVIDIA Corporation, 1.1.0)

/System/Library/Extensions

[Not Loaded] SONYDeviceType04.kext (Sony Corporation, 1.3.0.06030 - SDK 10.10)

System Launch Agents:

System Launch Daemons:

Launch Agents:

Launch Daemons:

User Launch Agents:

User Login Items:

iTunesHelper Application (Apple - installed 2018-07-11)

(/Applications/iTunes.app/Contents/MacOS/iTunesHelper.app)

CCC User Agent Application (Bombich Software, Inc. - installed 2018-06-29)

(/Applications/Carbon Copy Cloner.app/Contents/Library/LoginItems/CCC User Agent.app)

Dropbox Application (Dropbox, Inc. - installed 2018-09-18)

(/Applications/Dropbox.app)

Google Chrome Application (Google, Inc. - installed 2018-09-18)

(/Applications/Google Chrome.app)

ApowersoftHelper Application (? - installed 2018-04-13)

(/Users/***/Apowersoft/Mac Apowersoft Helper/ApowersoftHelper.app)

WDDriveUtilityHelper Application (Western Digital Corporation Branded Products Group - installed 2018-05-09)

(/Applications/WD Drive Utilities.app/Contents/WDDriveUtilityHelper.app)

WDSecurityHelper Application (Western Digital Corporation Branded Products Group - installed 2016-12-14)

(/Applications/WD Security.app/Contents/WDSecurityHelper.app)

Amazon Drive Application (? - installed 2018-09-18)

(/Applications/Amazon Drive.app)

Internet Plug-ins:

AdobeAAMDetect: (installed 2018-07-11)

FlashPlayer-10.6: (installed 2016-05-18)

QuickTime Plugin: (installed 2018-09-20)

AdobePDFViewerNPAPI: (installed 2018-08-16)

AdobePDFViewer: (installed 2018-08-16)

Flash Player: (installed 2016-05-18)

PMCADownloader: (installed 2016-08-14)

RL Secure Plug-In Layer: (installed 2016-04-28)

SharePointBrowserPlugin: (installed 2010-08-25)

User Internet Plug-ins:

WebEx64: (installed 2014-07-15)

ZoomUsPlugIn: (installed 2016-08-23)

UploadManager: (installed 2016-05-08)

ContentManager: (installed 2016-05-08)

RocketEngine: (installed 2016-05-08)

Safari Extensions:

3rd Party Preference Panes:

Akamai NetSession Preferences (installed 2018-04-17)

CUDA Preferences (installed 2018-02-08)

Flash Player (installed 2016-05-09)

FUSE for macOS (installed 2016-09-06)

Time Machine:

Skip System Files: No

Mobile backups: No

Auto backup: Yes

Volumes being backed up:

Macintosh HD: Disk size: 249.82 GB - Disk used: 185.51 GB

Destinations:

M*****************c [Local] (Last used)

Total size: 999.83 GB

Total number of backups: 30

Oldest backup: 2018-05-24 15:18:17

Last backup: 2018-09-20 19:08:51

Top Processes by CPU:

Top Processes by Memory:

Top Processes by Network Use:

Top Processes by Energy Use:

Virtual Memory Information:

Software Installs (past 30 days):

Clean up:

/Library/LaunchAgents/com.nvidia.CUDASoftwareUpdate.plist

/Library/Frameworks/CUDA.framework/Versions/A/Resources/compatibility_check

Executable not found

Diagnostics Information (past 7 days):

2018-09-21 09:47:46 Last Shutdown Cause: 0 - Power loss

2018-09-21 02:03:17 WD Drive Agent.app CPU (2 times)

/Library/Application Support/WD Drive Agent/WD Drive Agent.app

2018-09-19 13:41:18 mds_stores CPU (2 times)

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metadata .framework/Versions/A/Support/mds_stores

End of report

Moving and/or rotating didn't help, but thanks for the suggestion. Actually the problem now seems more serious... I decided I might as well buy an ethernet-to-mains extender set. I've just set that up, successfully got a connection to my router (with wifi switched off) and my download speed is still only 13Mbps!! Whilst my other devices can get 50-60Mbps.

Any idea what's going on? It's like the speed is being throttled on the iMac. I'm not connected to a VPN or anything like that...

iCare - I forgot to answer your questions in my last reply:

Have you always had the slow wifi performance issue with this iMac, or is this something new? If it's a new issue, did it start occurring after any changes to your network setup, a move, or service or updates done to your iMac?

No, I haven't always had slow WiFi. I believe the issue has appeared gradually over recent weeks. I haven't made any changes to my network setup, moved the iMac or router, or done any major updates that I'm aware of.

Cheers

Thanks. I still haven't worked this out 😕

I'm only getting 10-18 Mbps download no matter what - ethernet or wifi, VPN on or off. I should be getting about 50 Mbps... Upload speed is pretty much as expected.

I've tried unplugging all usb and thunderbolt devices. I've tried starting up in safe mode. I'm clutching at straws really. My other machine (identical hardware, with same software, used at another location) has no such issues.

Thanks all for the suggestions so far. Since last posting I’ve been on the phone and live chat to Apple and tried a few things,

Including:

-resetting SMC

-resetting VRAM

-being logged in as different administrator user account

-splitting out 2.4 and 5GHz WiFi SSIDs

-reinstalling OS

Anyway none of these helped and Apple said the next step was to bring it in for a service.

BUT... I then de-rigged my iMac upstairs, took it down and plugged directly into the router and actually got my full download speed.

So what would cause the speed in the upstairs room to be limited both on WiFi AND via Ethernet power line adapters? Some sort of interference I guess, but I have no idea. What could be the cause? And anyway, shouldn’t whatever component is affected by interference actually be better shielded? Is it likely that there is actually some hardware broken that basically should be less sensitive to interference?

The imac is one floor up and one room across from the location of the router. There are no metal objects between the two. If I test the wifi download speed in the same room as the imac on my iphone I get a good speed.

The ethernet cord goes directly into a mains adapter in a wall socket on the ground floor, next to the router. It comes out of an adapter directly in the wall socket in the upstairs room next to the imac. I've just had a look at my fuse box and note that my upstairs and downstairs mains sockets are on different fuses.

Thanks, but the problem persists whether VPN is switched on or not. Also, another machine I use elsewhere with dropbox and amazon drive is not negatively affected in this way.