Macbook Pro CPU problem - idle % consistently low, please help!

Question

Hi,
I've had my Macbook for about 8 months and never had any problems with it. Recently it started running very slow - freezing, mouse moving slow, typing response slow. I tried some solutions I found online (installing all updates, resetting NVRAM/PRAM, reindexing Spotlight, verifying disk permissions, entering purge in terminal). None of these worked. I checked Activity Monitor and the problem appears to be with the CPU, since every time the computer is running slow the Idle % is under 10%. Out of an abundance of caution, I uninstalled two Chrome plugins which were the only things I've installed in months (Adblocker and Disconnect.) I don't use any games or any other apps - pretty much all I do on my laptop is browse the internet on Chrome and use MS Word. I also have plenty of disk space, so I know that lack of storage is not causing this problem.
The only thing that has worked, at least temporarily, is shutting down, connecting to power source, and holding ctrl option shift power for 10 seconds, then turning back on (this was suggested in another thread on these forums.) The first time I did this it worked like a charm - my computer worked fine afterward, with the idle% back up to well over 90. However, it started running slow again the next day. I repeated the key process and again it seemed fine. Then again it slowed.
At this point I've tried the same solution several times and it doesn't seem to be helping anymore. Upon startup the idle% use in Activity Monitor is anywhere between 4% and 10%. The kernel_task is showing around 350% in Acitvity Monitor.
I have a very important test coming up at the end of the month and I'm studying 16 hours a day, and can't afford to be away from my computer for long. Is there ANYTHING I can do to fix this from home, or does it need to be taken into Genius under Apple care? If so, will they have to send it out and replace the hard drive, or will it be an easy in-store fix?
Any information would be appreciated! I am about sick to death of Apple products (my old first gen Macbook Air had to have its hard drive replaced twice and its screen replaced once.) If I can't find a solution I may have no choice but to up and buy a PC.

Answer 1

The kernel is using excessive processor cycles. Below is a partial list of causes for this condition.
Throttling
When it gets high temperature readings from the hardware, the kernel may try to compensate by interrupting the processor(s) to slow them down and reduce heat dissipation. This condition can be due to an accumulation of dust, to high ambient temperature, or to the malfunction of a cooling fan or temperature sensor. You might, or might not, see messages like the following in the Console window:
SMC::smcHandleInterruptEvent WARNING status=0x0 (0x40 not set) notif=0x0
The timestamps of those messages (if any) indicate the times, since the log was last cleared, when a processor was being throttled due to high temperature.
Note that if the problem is caused by a faulty sensor that reads too high, there may be no actual overheating.
The Apple Hardware Test, though not very reliable, is sometimes able to detect a bad fan or temperature sensor.
Using Apple Hardware Test
Encryption
Transferring large amounts of data to or from an encrypted disk image or FileVault volume may put an extra load on the kernel. If both the source and the destination are encrypted, the load may be doubled. If you transfer data from an encrypted disk image on an encrypted partition to another such image on another encrypted partition, the load may be quadrupled.
This issue probably doesn't affect late-model Macs with an Intel i-series, recent Xeon, or later processor. Those processors support hardware-accelerated encryption. You can determine what kind of processor you have by selecting About This Mac from the Apple menu in the menu bar.
Installed software
User-installed software that includes a device driver or other kernel code may thrash the kernel. 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 booting in safe mode (with the shift key held down at the startup chime.) Note, however, that disabling a system modification without removing it or booting in safe mode may not be as easy as you think it is.
Corrupt NVRAM or SMC data
In some cases the condition has reportedly been cleared up by resetting the NVRAM or the SMC. I can't confirm.