Chosen Solution
I just replaced the logic board, and now the fan intermittantly spins up to full speed (7500RPM) even when the computer is cold or just booting up. I was wondering if i maybe didnt get something seated right? or if there may be a bad sensor? I reset the SMC controller and the PRAM, didn’t seem to help, but the more I run it, especially getting it up to tempterature, the better it works. So maybe it will fix itself as the heat sink seats itself into position. Just wondering if anyone has experienced this before and if anyone has any suggestions? Update (11/14/2017)
The left fan is intermittently running at max speed, but it changes by the second, it will go a few minutes running normally, but then jump up to 7500 for a few seconds and drop back down, all while the right fan never changes, unless the overall temperature of the heat sink increases, then the right one will speed up as expected
It appears the right fan is not spinning up at all which is why the left is going full speed to compensate for the failing right fan. Either something is jamming the blades just enough to slow them down or the motor is failing. It’s also possible the left fan tach is failing so it thinks it needs to run hard. I would first see if an SMC reset solves this or try replacing each fan with a spare.
