Chosen Solution
I recently did a teardown top to bottom clean on my Macbook Pro, and accidentally ripped the trackpad cable, which contains a temperature sensor. Due to that, the fans run at full blast and the CPU is throttled because it believes something is at 100C, however using an app such as MacFansControl I can confirm that that maximum temperature is 40C, so there is no need to throttle or run the fans at full speed. Using Activity Monitor I found that Kernel_Task is using all of the available CPU, and causing lag. The lag causes the system to be completely unusable, and I would like to stop this from happening as I rely on this laptop to work from home. Edit: I forgot to mention that I am running High Sierra, 10.13.6
Replace the Trackpad Touchpad Flex Cable - MacBook Pro 15" A1278 Mid 2009 2010 2011 2012 https://www.ebay.com/itm/For-Macbook-Pro…
