kernel_task CPU usage too high on fresh HIgh Sierra install on A1466 Early 2014 Macbook Air

For reference: If kernel_task is using a large percentage of your Mac CPU - Apple Support

Lacking any software causes easily identified with Activity Monitor, a runaway kernel_task is always caused by one or more of the following:

• a failed or disconnected temperature sensor
• cooling system inefficiency (an inoperative exhaust fan on Macs so equipped, possibly clogged with dust, including the heat sink)
• a worn out, missing, disconnected, or non-Apple (user-installed) battery on portable Macs
• similar hardware-specific causes including internal hardware additions or modifications, external USB and other connected devices, or the driver software required to use them.

Determine if the same problems occur in "Safe Mode": How to use safe mode on your Mac - Apple Support. If it continues without loading any potentially troublesome software, you have effectively ruled out software as a cause. That leaves the existing water damage as the only possible cause. Identifying and replacing the defective hardware will be required.

Water damage can be repaired, but it is extremely time-consuming and tedious, with a high probablility of damaging something else in the process and an equally low probability of success. I don't believe the DC-in board is related to the CPU powermetrics data anyway.

Component-level troubleshooting and repair is a lost art. That's why Apple won't bother replacing anything other than major components such as logic boards and displays. It's not worth it.

There are a thousand failures for every YouTube success story. Don't let me dissuade you though, given enough time and determination anything can be fixed.

wongkarcanada wrote:

There is no obvious water damage internally. The laptop does seem to work, albeit the fan is at full blast, and it is slow as molasses.

There is obviously some liquid damage to the Logic Board since you are experiencing system behavior typical of liquid damage. If you look closely with a magnifier and strong light you may see small signs of corrosion somewhere on the Logic Board or other internal components. Corrosion will appear as whitish, greenish, or even bluish specs on the pins & solder joints of the surface mount components or on/in the connectors. Sometimes corrosion is significant & easy to see, while other times it may be as small as a dot (aka period) if it is on an extremely small component where the pins are very close.

On the older MBAirs, liquid tends to hit the I/O Board & I/O Cable connections, as well as along the back edge of the Logic Board. The back edge of the Logic Board is also where the SMC chip & JTag connector are located. You are unlikely to see any corrosion with the SMC chip since all of its solder joints are beneath the chip itself. Besides, the SMC chip may be Ok and it is just damage to the power circuitry supplying the chip. The Trackpad connector and Trackpad IPD Flex Cable are also typically damaged with liquid.

At least the seller was being honest about liquid damage and only selling it as a parts system. That is refreshing there are still honest people out there.

You have an eleven year old computer that has admittedly been water damaged.

Write it off as a loss and move on.