Ive always struggled with this problem I almost always just let my mba sleep but sometimes when i open the lid my mba decides to run really hot and of course the fans run faster and noisier. Checking the process monitor, (all processes selected, not just user processes) there is nothing using the cpu. Average CPU is typically around 1-4% yet the cpu temp is around 78-88c and the fans > 3,500rpm I don't know what is going on? The only thing is the mba is connected to an external display via the thunderbolt to HDMI adapter. I've tried an SMC reset in the distant past but the problem always returns and i believed that to only cure issues when the fans run quick without heat from the CPU. Any ideas?