Chosen Solution
Seem to be having kernal_task thermal throttling. Where CPU is throttled to 0.8GHz and fans run max. Issue is intermittent so only happens sometimes but it massively frustrating. All sensors are fine. Had previously SSD fitted but had stock HDD refitted to no avail. Confirmed that mac is not overheating. How would I disable the thermal throttling?
You have a hardware level issue, it’s not an issue with Mojave.
