I recently realized that there are a lot of people still having issues with the microcode issues on Arch Linux regarding the changes to the Intel bootloader so this is just a quick tutorial that explains how to fix it. I wrote this tutorial as a reply on the Antergos Forum over a year ago so I haven't tested this solution in over a year but after looking over it again I don't see any reason why it wouldn't work. Anyway, here is how to fix this issue.
1. You need to update your pacman database and it will ask you to update packages which is fine, go ahead and do that.
sudo pacman -Syu
2. Now install the intel-ucode package.
pacman -S intel-ucode
3. The next step is to update the grub.xfg file to include ucode. The following command will open the file grub.cfg in gedit as root so you can edit it.
sudo gedit "/boot/grub/grub.cfg"
4. This file will have a lot of lines that were auto-generated by Grub. Search for the following, “initrd”. You will find two instances of that in the file. The first instance will include the term “initramfs-linux.img”. There you will add “/intel-ucode.img” in front of it so it looks like:
initrd /intel-ucode.img /initramfs-linux.img
5. Save the grub.cfg changes and restart…you should be back up with everything up to date.