You likely have a hardware issue, please take the computer in to have it serviced. I suspect that a fan sensor has failed. You can take it to an independent Apple Authorized Service Provider and they will diagnose it and fix it on your approval. To locate an Apple Authorized Service Provider please click Apple Authorized Service Provider Locator (AASP) & Genius Appointment
If you have not already, please reset the NVRAM 2-3 times and then test. How to reset NVRAM on your Mac For best results do this with all external peripherals (External Hard Disks, hubs, etc...) disconnected and do the resets back to back.
Good luck!