So I have a mid-end PC which the vanilla New Vegas would set me up on Ultra High settings. Playing without any tampering to the ini and without mods is no problem, of course.

However, I tried some ini tweaks, mostly from the Tweak Guide by Koroush Ghazi, and also playing with mods. Not an overwhelming bunch of them, per se, and always highly-endorsed mods. 4GB Enabler is on too plus the ENBoost Speedhack which works very well for me when I was still playing Skyrim.

Lately, I've been noticing a considerable drop in my FPS. It happened relatively not long after I started a new playthrough. Without ini tweaks and mods, I get a stable 55-60 FPS. But most recently, it was like 19-22 FPS out of the blue.

Any ideas, guys?
I'm looking for comprehensive answers on what can cause FPS drops.
Something you've found out from and dealt with in experience.

My Specs:
> AMD Phenom II X4 955 Quad Core Processor @ 3.2 GHz
> Gigabyte GA-78LMT-S2P Motherboard
> Windows 7 Ultimate 32-bit (6.1, Build 7601)
> 4 GB RAM DDR3
> Radeon HD 4850 2GB DDR3
> Seagate Barracuda 500 GB 7200 rpm S-ATA Hard Drive

I'll post my Load Order soon.

I don't know if I can help you, but here are my experiences...

Seeing that I've ranted millions of times at my game for countless CTD's and freeze incidents, it was until I was making a mod where it spawns enemy mobs from the other side after each one is killed. I did this with two factions warring against each other, added explosive vehicles and shit, but it was until then I noticed not only was my game lagging, seeing texture bugs and invisible meshes, even a noticeable FPS drop, it suddenly hit me with the confirmation error saying "Out of memory" and CTD.

So I've come to the conclusion that Fallout New Vegas, or any of Bethesda's games run solely on memory. The engine can only take so much before it refuses to function, so I grabbed the large-address-aware 4GB enabler or patch, either one works fine but I don't think the patch works for FONV.

Here are my possible solutions:

-You may be running too many mods(If any)...
-Close any background applications(Except Steam, you can't play Skyrim without Steam unfortunately), such as Firefox, Chrome, or whatever. It should give you a significant boost in FPS.
-You very much likely need more RAM so your game can handle 4GB like a charm. I got 8GB of RAM on my system so far, and it flies like a dream, since my OS is W7 Ultimate Service Pack 2 and equipped with a six-core processor. It also supports both 32 and 64 bit versions. So a suggestion, I advise you'd save up for the specs needed to upgrade your PC if you consider it.
-You could try various applications such as razer's game booster that my friend RGCaboose(Hugo) uses. Also defrag your PC often. You don't have to, but it's considerably recommended.

That's all I know. Hope this helps...

@ Admiral Slyther

Counter to your possible solutions:

> Running too many mods? I don't think so. Around 100 mods or so. Is that too many?
> Closing background apps? Done that everytime before I start playing.
> More RAM? Possibly. But then I need to upgrade to 64-bit Windows and that will take too much effort, at least for now.
> Use the Game Booster App? I, in fact, do use it. Hehee...

Thanks anyway for trying to help.

@ roflcopter

I'd say it's continuous. The last time I checked, my FPS was ranging only between 19-22.
I do cap my FPS at 45, but I don't turn off the V-Sync. I don't like the screen tearing effect that comes with turning it off.
ENB? No, I don't use any ENB graphic enhancement. I only use the ENBoost.
Plugins? Around 100. Haven't really checked the exact count. But certainly not more than 120.

Okay, mate. Looking at your advice, it seems that the problem isn't something I don't already know. Will try to do a more thorough sweep on my FNV installation.

More advice would still be appreciated, though. If anyone thinks that they know some things I don't, please don't hesitate to reply here.

Thanks!