kernel_task 400% and hardware test show faulty sensor.

Hi guys , I have MacBook air early 2014 i5 processor from few days i have been facing this issue of kernel_task is eating Cpu upto 400% and computer is running very slow ,

and it also takes long press power button like 7-8 seconds to startup ,

when i did the hardware test it shows the problem in sensor but if it is problem in sensory mac should be heating but in actual it is not the people are saying that you need to replace whole of the logic board .

what should i do ??