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Model A1419 / Late 2013 / 3.2 & 3.4 GHz Core i5 or 3.5 GHz Core i7 Processor, ID iMac14,2

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iMac high CPU usage running very slow by kernel_task

Hi,

Got this issue with this iMac which first looked like an easy job it was running slow and still had old HDD which was bad as well, full of bad sectors.
However problem seems to be much deeper than this.

Installed new SSD. OS took almost full day to install (Recovery mode is lagging as well). After installation iMac still running ultra slow. Activity monitor shows that all CPU usage is taken by kernel_task.

Started looking whats causing the issue.
Everything I done to this iMac but the problem is still on going:

Tried with other RAM.
Replaced Thermal Paste. (Computer wasn't even overheating)
Tried with original fully working HDD
Tried with original apple pcie SSD.
Tried external OS through adapter.
Internal diagnostics, etrecheck don't find any issues.
New front camera where ambient sensor is.
Thorough look on motherboard to find any physical damage or bad components (clean as a baby)
SMC, PRAM, NVRAM resets.

When computer sits not used for a while first boot seems to work fine computer works but no long after kernel_task starts again to take all the cpu usage and iMac starts running really slow again.

Anyone maybe have ran in to this issue and found a solution or might give heads up what more I can check.

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I would run the onboard diagnostics, restart the system and with a USB keyboard hit the D key to enter. Here’s a reference on the special startup keys Mac startup key combinations let us know what you got for errors. Etrecheck really doesn’t offer a deep enough diagnostic view. The only App which does is TG Pro which I strongly recommend getting the full version as you can monitor your systems health via the thermals.

Also what version of macOS are you running?

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Tried with Catalina, High Sierra Same issue.

Onboard diagnostics shows No issues found.

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@maw38972 - Let’s backup here… this was a Fusion driver system? Having both a HDD and Blade SSD? If that’s the case the drive is looking for its mate drive. The firmware also gets into the mix here as well as you really need to unlink the drives before hand.

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@danj Originally there was just a HDD drive. No fusion nor blade SSD.

I was just trying all possible choices of drives to see if issue can be resolved.

So first

Installed SSD didn't help.

Tried again with original HDD didn't help

Then tried just with blade SSD didn't help also.

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@maw38972 - Good! So that gets into the issue of the Apple vs standard HDD SATA drives or even a 2.5” SSD. Apple had custom drives made for them as they wanted access to a temp sensor within the drive so SMC s\could monitor it to alter the fans speed. While Apple finically abandoned this as they finally got the ISO group to alter the standard so the older IRQ method was altered into a constant feed. Apple did alter its system firmware to leverage the newer method. But not all drives offer it. Which the. Gets into how to add the needed sensor to prevent the issue, here’s the needed part iMac Intel 21.5" and 27" (Late 2012-Early 2019) SSD Temperature Sensor. This cable is required if you are using a SATA drive. If you are using a Blade SSD then the sensor is not used but the header jumper is needed if the system was sold as a Blade SSD system only or configured as a Blade drives system after converting from a Fusion Drive setup.

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