@VRam Try this: Z97I-PLUS_Mod.rar (5.0 MB)
I suggest for you to downgrade your bios version 2 or 3 versions lower than current bios, and flash using AFUWIN /GAN method or AI-Suite method with the bios mod. If you decided to use the AFUWIN /GAN method, afaik in my own test, it wont update the ME Firmware, just the bios region, and i never tested the AI-Suite Method, so i gave you 2 files, 1 for AFUWIN /GAN method (.ROM), and 1 for AI-Suite Method (the .CAP). For AI-Suite, i dont know either AI-Suite 2 or 3 will do the trick. You can find AI-Suite 2 here (Choose Windows 8.1 64Bit for the OS, and scroll down to Software and Utility section), and AI-Suite 3 here (Just scroll down to Software and Utility section).
Be sure to FULLY Backup the current bios first, as it contains your motherboard credentials, you can use Intel FPT from this forum to dump it (just do fpt.exe -d Backup.ROM if Possible to dump the whole bios chip), or use AFUWIN /O Backup.ROM, and save the bios backup to anywhere you please, but at least consider putting it in your flash drive.
If flash is successful, please try to Disable CSM (and make sure no legacy settings are enabled except Legacy Usb settings), enable igpu (if you’re not using Xeon), and enable above 4g decoding, see if iGPU works under UEFI with Above 4G Decoding Enabled.