Choose the right folder depending on the patch you use and select between 3 quality options for performance/quality balance changes:


-High: All effects are enabled on the highest needed quality. Recommended for nowadays hardware and also if you want to create screenshots or a video. It's installed by default.

-Medium: All effects are still enabled but with reduced quality. Not much difference in visuals but performance should be slightly better. Recommended for gameplay or mid end hardware.

-Low: Disabled Ambient Occlusion, Detailed Shadow and a few other minor things. Still looks decent but you can tell the difference. Performance should be better.



If you want to improve performance even more:
 
-If you use patch 7/8, EFLC or the latest Steam/RGL version of the game don't put shadows on very high. Use high or medium instead for a good performance boost.
 Regarding which patch/version (Including DLC's) of GTA IV you're using DON'T put the view distance and detail distance sliders on 100!
 Putting both sliders on 100 impacts performance a lot. Console versions of IV are using a value between 20-25. If you have a decent PC I would recommend a value between 30-50.
 I wouldn't recommend to go above 50. For vehicle density it depends on your CPU and RAM I guess. I would recommend to leave it between 20-50. Depending how much traffic you like. 


-You can try to disable ENB's EdgeAA (Anti Aliasing) by open enbseries.ini or by pressing shift+enter ingame and search "EnableEdgeAA" inside the [ANTIALIASING] section.
 I haven't noticed any performance changes by disabling ENB's Anti Aliasing but on lower systems this could help to improve performance a little bit more.


-Decreasing the resolution also helps a lot to improve performance. 


-Patch 1.0.4.0 should be more performance friendly compared to other patches and this mod also looks better on patch 4. If you have performance issues use patch 4.


-If non of these things are working for you to make GTA IV playable at a smooth framerate I can recommend my natural timecycle graphic mod which haves no performance drop.
 Link: https://www.gtainside.com/en/gta4/mods/160838-dayl-s-natural-timecycle/
 Don't combine DayL's Natural Timecycle with iCEnhancer 3.0 Natural! You have to uninstall iCEnhancer 3.0 Natural before installing my natural timecycle mod.