Kernel.task using 300% of CPU. MacBookAir mid 2013

Question

Hi
I have a MacBookAir mid 2013, 13-inch.
Starting my mac up after sleep to weeks ago, it behaved very strange and has done it since that day. The fan turns on at full speed, and the Kernel.task operation is taking up 300% of the CPU, or in other words the system is constantly using between 65 - 80 % of the memory, hereby making the Mac very slow, and useless to use for anything. Also at the same time the sound disappeared, in the system configuration there is no output audio to select.
I have tried a lot of things in order to fix this problem, based on things I found in the discussion forum here. I have tried memory cleaner, to remove sound files, to remove plists (as many suggests, but for this MacBookAir6,2.plist, does not exist), I have formatted my hard disk and reinstalled the original OS X system (Mountain Lion), and the upgraded to the current version (Yosimite). But nothing has worked.
Does anyone having the same problem? Or know how to fix this? Anyone been in contact with Apple related to this problem?
Best regards
Morten

Answer 1

First, get rid of "Memory Cleaner," which is useless at best. Then see below.
The kernel is using excessive processor cycles. Below are some possible causes for the condition.
Throttling
When it gets high temperature readings from the hardware, or low voltage readings from the battery of a MacBook, the kernel may try to compensate by interrupting the processor(s) to slow them down and reduce power consumption. This condition can be due to:
☞ a buildup of dust on the logic board
☞ high ambient temperature
☞ a worn-out or faulty battery in a portable
☞ the malfunction of a cooling fan, a temperature sensor, a voltage sensor, or some other internal component
Note that if the problem is caused by a sensor, there may be no actual overheating or undervoltage.
If the computer is portable, test with and without the AC adapter connected. If kernel_task hogs the processor only on AC power, charging is causing the machine to heat up. That behavior may be normal for some models. CPU usage should drop when charging is complete.
Apple Diagnostics or the Apple Hardware Test, though not very reliable, is sometimes able to detect a fault. For more thorough hardware testing, make a "Genius" appointment at an Apple Store, or go to another authorized service provider.
If nothing is wrong with the hardware, then whatever you can do to improve cooling may help.
Installed software
User-installed software that includes a device driver or other kernel code may thrash the kernel. That category includes virtualization software, such as Parallels and VMware, as well as most commercial "anti-virus" products. Some system-monitoring applications, such as "iStat," can also contribute to the problem. You can test for this possibility by completely disabling or removing the software according to the developer's instructions, or starting in safe mode. Note, however, that disabling a system modification without removing it or testing in safe mode may not be as easy as you think.
Corrupt NVRAM or SMC data
Sometimes the problem is cleared up by resetting the NVRAM or the SMC.
External display
Connecting an external LCD display to some MacBook Pro models while the lid is open may cause this issue. If applicable, test by closing the lid or disconnecting the display. You might get better results with a newer LED display.