VirtualBox consuming 100% CPU even when the guest is idle

I had this issue with 2D Video Acceleration enabled. Once I disabled it in the Virtualbox machine settings, the host high CPU usage was gone.

Also try this alternative where the guy disables "Nested Paging". It worked for me reducing 16% of CPU usage.

If you’re not familiar with this setting. Shut down your virtual machine so that you can edit the settings. Then go to the system tab, click on Acceleration and then uncheck the Enable Nested Paging checkbox. Click OK and start the virtual machine up and you should quickly notice some performance improvements.

Your processor does not offer hardware-assisted virtualization so VirtualBox is using software-based techniques, which will use more CPU time and make everything slow.

Read more about it here.

None of the above worked for me with an old Acer laptop, 2 x86 CPU cores; 3 gigs of RAM, running Win XP SP3 Host, and Win 7 guest (on VirtualBox 5.0.24). My "Acceleration" tab is disabled, so "Nested Paging" is not enabled. Also "Remote Display" was by default disabled. The VirtualBox panel had automatically disabled selection of any number of CPU cores, and was stuck on 1 CPU (although my Host system tray clearly shows the involvement of both CPU cores). Also the Windows Update of the guest machine was already disabled.

However, my guest machine took up at least 50% of CPU even when idle.

My solution? The problem solved only when I enabled both the 2D and 3D accelerations in "Settings -> Display -> Screen" and then increased the "Video Memory" in the same tab ("Settings -> Display -> Screen") to the maximum 256 meg allowed.

Once the guest machine received a good deal of video memory from the RAM, the CPU usage dropped to a nice 10% to 20%.