I am having a very strange issue with my fan on my 2013 MacBook Air. For no apparent reason, the fan started running at maximum speed when I was using the computer. Thinking it was just something weird from my current session, I rebooted the machine. The fan activity didn't stop. I next tried to completely shut the computer off and turn it back on. A few seconds after the power chime was heard, the fan kicked in once again. I went into Activity Monitor and looked at the CPU section. According to Activity Monitor, Kernal_Task was using 200% of the CPU. I also found that about 20% of the CPU was idle even though I wasn't doing anything that would warrant that kind of processor load. This appeared to solve the mystery of system lag I was experiencing as well. For some weird reason, the processor was almost maxed out. I next tried to reset the NVRAM and SMC, but that didn't seem to help.
Having concluded it was a software issue, I backed up all my important data and performed a clean install of Sierra. The fan was active while performing the install. I also noticed that the install took about an hour and a half which I found really unusual. I figured it had something to do with the increased CPU activity. Well, I got the OS installed and I'm having the same problem. Every time I turn the machine on, the fan kicks into high gear. I've tried resetting the SMC several times by connecting the power adapter and pressing and holding control, option, shift and power for about 10 to 20 seconds when the machine was off. This didn't seem to help. What's going on? Is this a hardware related issue? Can I do anything else before I'm forced to take this to an Apple Store? I've had this computer for a little more than three years and I'm pretty sure my warranty expired years ago. Any advice/tips are greatly appreciated.