These steps will fix two Fallout 4 issues: A “laggy” mouse that resembles acceleration or smoothing and the locked 60FPS cap.
1. Launch Fallout 4 and click “Options.”
2. Configure the options to your liking. Close the menu items and click “Exit” to quit Fallout 4 completely.
3. Navigate to \My Documents\My Games\Fallout4\.
4. Create a backup of Fallout4Prefs.ini (copy/paste locally)
5. Right-click Fallout4Prefs.ini, click Properties, and ensure that the file is not presently set to read-only. This should only happen if you've been here before, otherwise it's writable.
6. Edit the file. Ctrl+F for iPresentInterval.
7. Change iPresentInterval=1 to iPresentInterval=0.
8. Save & close the file.
9. Right-click Fallout4Prefs.ini, click Properties, and check the “Read Only” box, then apply your settings.
Fallout 4 will no longer be able to modify game settings at startup, so you'll need to make the file writable again (reverse step 9) in order to change resolution, shadows, or any other settings. The purpose of locking the file is so that iPresentInterval is not reset, because Fallout 4 resets the file at each launch.
There is a Fallout4Custom.ini, which we suspect is an override for some other file. We tried adding iPresentInterval here, but it didn't seem to take. Success was only achieved with Fallout4Prefs.ini.
FPS can now exceed 60. As a side effect, the mouse should now feel more natural (like raw input) and the lag / smoothing / acceleration effect should dissipate with higher framerates.
In Skyrim, it used to be the case that adding bMouseSmoothing=0 to the [Controls] block in .ini files would remove smoothing, but we've been using the above solution instead for Fallout. If you find something that works – and most things that worked in Skyrim & New Vegas should work here – post it below to help the others who land on this page.
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- Steve "Lelldorianx" Burke.