System (ACPI.sys) is always using about 15-20% of my CPU

I have a 13" Sony Vaio laptop (model SVS13A1C5E) and I upgraded it to Windows 8 with a fresh install, after upgrading I installed Win8 drivers listed here.

Now I have a problem with the CPU usage (it drains my battery), in Task Manager I can see that the "system" process is always using 15-20% of my CPU (i7-3520M) and looks like the usage is on a single core. This is what I found by using Process Explorer, the usage comes from ACPI.sys which looks like it is generating a lot of hardware interrupts.

By doing some research I found out that should be an issue with some drivers but I don't know how to figure out which one is causing this. (Please do not tell me to "upgrade" to Windows 7)

Solution 1:

I had similar issue with Dell E6540, 4 cores, one core permanently at 100%, process: System, thread: acpi.sys. Thanks to @ThePosey I tried to turn off Device Manager -> Network Adapters -> Intel(R) Ethernet Connection I217-LM. Process usage immediately dropped to 1%. When turned on -> one thread started to work at 100% again. Then I noticed that when I switched Power Options -> Power Plans, CPU usage characteristic changed (one core 100% -> 80%, other core 0% -> 50%, depended on the selected profile). Then I researched the problem further and found out a solution: Network Connections -> Intel(R) Ethernet Connection I217-LM -> right click Properties -> Configure -> Power Management -> section Wake on LAN -> disable Wake on Magic Packet AND Wake on Pattern Match. Process usage immediately dropped to 1%, problem solved.

Solution 2:

I fixed it! The problem was the BIOS, I updated it after installing Windows 8 (it was a win8 specific update) but it looks like it contained some bugs. If someone have this problem and needs to revert the update here you can find some bios mods based on the original version but also the stock one: http://forum.notebookreview.com/sony/677079-sony-vaio-s-bios-mod-gt640m-le.html

Also: With the updated bios version I was not able to see my Bluetooth, now it's working. Thanks all for the help given.