if Windows 7 have troubles to find updates, causing high CPU or RAM usage with the process Svchost.exe, it is due that Windows Update was not able to update automatically the Windows Update Client.
in this case, you need to download the update manually, this is the most recent version for now: https://support.microsoft.com/en-us/kb/3138612
Note: if you have troubles to install this update, stop "Windows Update" service, and fastly try to install the update.