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Stutters when using PSX.NET.MSFS.WASM

Started by macroflight, Mon, 18 Sep 2023 20:20


Ever since upgrading my sim computer from an old 6-core AMD CPU to an Intel 13900K and a 4090, I get a more or less stuttery experience whenever I use PSX and MSFS together using PSX.NET.MSFS.WASM. Pure MSFS works well (e.g with PMDG737 or Fenix).

The problems seems to be CPU-related. It's worse at complex airports and worse with lots of VATSIM traffic.

The stutters are worst when turning the aircraft while taxiing, but there's the occasional stutter when moving in a straight line as well. The aircraft can also do strange things on rotation - jerky movement, doesn't feel quite right.

If I turn down all MSFS settings and make sure no CPU core gets anywhere near 100% utilization, things improve. But I have to turn down the settings to very low levels to get things stutter free. It feels like there's something I'm missing here, this hardware should perform better...

I've tried using Process Lasso to e.g force PSX to run on the E-cores or make sure the PSX.NET.MSFS router and client run at high priority but it didn't really improve things.

The main PSX instance seems to run fine, it shows 60Hz (set to 60/3) even when stuttering is really bad.

My MSFS settings - well, I've tried just about any combination I can think of... usually with vsync on as that keeps cpu utilization lower, which seems to help.

Is anyone running a setup with MSFS, PSX.NET.MSFS.WASM and PSX on the same computer and have a stutter-free experience? How? :)


- One PC, Intel 13900K, nvidia 4090, Windows 11
- Screen 1: 2560x1440: fullscreen MSFS
- Screen 2: 1200x1920: vpilot, vatspy, ...
- Screen 3: 1440x2560: one PSX instance
- Screen 4: 1920x1080: touchscreen with three PSX instances
- Power limited in BIOS (long and short duration) to 125W (which seems to be what the AIO cooler can handle)
- Power Plan: high performance


I experience the same issue, but it started with some of recent ...WASM updates - about when the new exterior model came out. As you mention, it gets especially noticeable when turning on ground, takeoff/landing, and with AI/Vatsim planes. Also sometimes the whole MSFS seems to get stuck for few ms.
I also now notice that when the barometer setting is changed, MSFS readjusts visually the AGL.

Previously it was completely stutter free experience, even with settings borderlining Ultra in MSFS and LOD 150-200.

I am runnning PSX and MSFS on single machine with AMD 5800x3d and 6800xtx.

Gary, where can I get the «old» files to make another comparison?

Gary Oliver

Oh... that's not good, the old link is still available on the old thread there (and what I'm still running in my own sim for the internal visuals)

Anyone able to confirm?


I'm not sure if this helps you, but I have no stutters. I run with medium settings in MSFS, I think. And it's an Intel i7 11700k, with Nvidia 3060 Ti.

Everything is running on one PC: MSFS (no 3rd party scenery), PSX, Navigraph charts + Simlink, RealTraffic.

3 x 32" monitors, 1 external CDU with 800x600 monitor.

I would get stutters with MSFS maxed out on ultra settings, but I'd expect that.
Will /Chicago /USA


I'm not having any issues with a 6 year old Windows 10 machine with 7700k processor, 32 gig memory, air cooled and a 3060 card with a single 32 inch monitor.  I always run Vatsim and Navdata.  I set mine system up like Gary suggested.  My MSFS2020 setting are pretty much middle of the road.   

Your problem almost sounds like an anti-virus problem.  I don't run one on my gaming machine.  I download everything to my main network computer and then copy it to my gaming machine. 
Grace and Peace,



It's encouraging to hear I'm not the only one with problems, and that others are stutter free. :)

I just spent two hours trying to come up with a simpler setup that still stutters. Live weather off, no addon airports, ... but it's still remarkably stutter free. As long as MSFS can keep the 60 fps I asked for, it's silky smooth. When I crank up the settings or go to a complex airport fps drops a little and there's some very minor stuttering, but nothing like the big jumps I saw on my VATSIM flight yesterday (Vectors to Copenhagen event, so lots of traffic).

But I've also had really bad stutters earlier when there was no or very little traffic.

I'll keep digging...


I've also noticed stutters but not been able to track them down. I think it's the processor AMD 7950x3D, but I also have an RTX 4090 which seems to be a common thread online. Running over a network I've tried various things such as replacing the switch, packet loss tests, removing the internet and all but the Aerowinx and MSFS machine, Aerowinx boost running on the visuals computer, Aerowinx at 60/3 60/2 and 73, various computer tweaks.

Tried setting the setting to the lowest and they still seemed present. I did find plenty of others on forums using similar speced machines who have stutters so figure it's a MSFS issue? I do seem to remember an old version feeling very smooth but maybe I just didn't notice the stutters in testing. Been wanting to test on my old machine but I don't fly often.

Tried locking to 30 and 60 fps.

Maybe related but if I roll the wings enough I can force a little snap jump as seen in the video'

Generally use XPlane as I like to save the weather but hope the feedback is of use now knowing I'm not the only one?


I think the motto of MSFS should be "the flight simulator of today, for the hardware of tomorrow."

Ever since the 1990's, the Microsoft flight sim software has let you do things to it--whether moving the sliders to the right, or adding custom packages, or linking things together online--that kills its fluidity. 

Two observations...

1. In two or three years, there will be advances in CPUs and GPUs that will allow a smooth MSFS 2020 experience, but by then everyone will be using MSFS 2024 and we'll be back where we started.

2. A real advance would be to have an AI engine built into the sim that dynamically adjusts settings in real time based on user preference. You could give it a main priority, such as fluid motion, and then sub-priorities to peel back, in order of preference, when the main priority is at risk. No more moving sliders and experimenting. No more issues where "big" airports stutter more than small airports. No more manually balancing CPU vs. GPU loading, disk read time, buffering, internet connectivity, object density, and all that.
Will /Chicago /USA

Gary Oliver

Can I ask those experiencing stutters to enable dev mode and enable WASM debugging - and see what the frame times for the WASM module are?

I am expecting under 100 microseconds (0.1ms)



Looking at that screen on the runway there's multiple options

Simobjects total time hovers around 16.6

On the drop-down section they seem to be mostly 0.0 however the max values are higher

Panel_service_pre_update is 151.0
Panel_service_pre_draw is 62.0

User objects total time is about the same 16.6 but I did see it hop to 30 (still far less than 100)

Panel_service_pre_draw is the only outlier here with a max of 173.0 and the average hovers around 14.5

During flight similar numbers, didn't notice any spike during wing snapping. In game fps was locked at 30 using vsync and didn't budge.


Reverting to old version seems to have resolved stutters at my place. Will check more.


Short status update from me: I have not been able to reproduce the really bad stutters I saw last week.

I tried both doing more flights with the same settings (but no really busy airports yet) and some flights using much more aggressive settings (no vsync, graphics Ultra, higher rendering scaling, ...). Yes, minor stutters with extreme settings but nowhere near as bad as earlier. And those stutters felt more like something internal to MSFS than related to PSX.

I did check the WASM debug window. No really high numbers, but since I didn't see any bad stutters that doesn't mean very much.

I'm so annoyed I can't find a way to reproduce the problem... yet it popped up very often before. I don't think it's antivirus, Windows Defender is active (can you get rid of it in Win11?) but set to ignore the entire disk.