Long term problem, so far. iMac, mid2010, Mavericks 10.9.3. Issue existed in Lion and Mountain Lion. Under energy saver settings, on boot-up, iMac will go to sleep as programmed. After a while, it will not go to sleep under energy saver, even with no running programs. Unplugging wired network, shutting off wireless network -- no help, it's not a network wake up. Unplugging all USB devices and Firewire disk drives -- no help. Symantec anti-virus is installed, and all functions turned off (also this problem existed before anti-virus was installed) -- no help. Manually setting sleep mode, works fine. Activity monitor shows exactly the same daemons and programs running when auto sleep works as when auto sleep does not work.
I'm baffled, and don't know what to look for next. Any advice? Thanks!