I'm using Windows 8.1 64bit.
I had an issue with the Windows Modules Installer Worker using a high percentage of CPU when no updates were available. I ran the Windows Update troubleshooter and it seems that problems were found and fixed:
Potential Windows Update Database error detected 0x80070490
Possible issues may prevent Windows Update from keeping your system up to date.
Windows Update components must be repaired
One or more Windows Update components are configured incorrectly.
The issues with Windows Modules Installer Worker's high CPU usage stopped. However, a few hours later it started again. Sure enough, when I ran the troubleshooter again it showed the same errors had been found and fixed. I re-ran the troubleshooter straight after "fixing" and it's claiming the same errors are present and have been fixed.