Thank you so much for replying. My laptop was finally usable after a horrible 8.1 update (which I had to reinstall everything from bare metal) and now it is unusable again after Update 1.
Step 1 - I ran the DISM tool three times. It found corruption, and then fixed it. I checked for updates again, there were several and I installed them. Reboot. Same problem. After about 7 minutes of 100% disk, I am back to the Windows Module Installer Worker using 50% or more of the CPU for several hours now.
I tried the built in troubleshooting. It found an error with the update and fixed it. Still have the same problem.
Step 2 - sfc refused to work. It says another servicing or repair operation is currently running...