Visual Studio 2013/2015 Idle CPU usage

Solution 1:

Had this same problem. Processor constantly at 45-50% even when the IDE is completely idle.

Turns out the problem is the Microsoft Git Source Code provider.

I turned that off and processor dropped to 0 and the IDE became much more usable.

Solution 2:

In my case disabling Telerik ASP.NET MVC Extension solved high CPU issue.

High CPU load started on solution load and didn't drop (40% with one, 80% with two solutions) until VS was closed or even sometimes after (had to kill the process).

Tools->Extensions and Updates->Installed, find the extension and click 'Disable'.