So the last few days I have been having a weird shudder from my engine at low rpms (800-2500ish). It only happens when I am idling at a light, and when I start to accelerate (especially under more load). It is not constant, but and different times the engine will shake once, and kind of pop like it didn't fire on one cylinder, or backfired. When it does it under acceleration, the car hesitates and almost feels like it wants to die, sometimes even "bucking" a tiny bit. It is winter here in Utah, so I'm almost positive it isn't the heat soak bucking I have heard about. My car is a 2000, on its second engine, with a berk 3" cat back, and an AEM cai. Also, I don't know if this is related, but the cat on it doesn't work, so an 02 simulator was installed. I searched around, but so far have not found a problem that sounded exactly like mine that someone else experienced in the forums.

 

Here is a video of how it sounds at the moment. Its not making the popping, and hesitating like it was, but it does sound really "mushy." Im going to go check the coils and spark plugs just to be sure.
https://www.youtube.com/watch?v=PENdkABu82A

 

Is the cat broken internally ?, that will certainly cause issues.

 

Sounds kinda like exhaust leak. If your cat is somehow broken then you might get a code for it and it might also rattle when shaken.

 

Apparently there is an "o2 simulator".

 

I guess I got too worried about it haha. I found a very worn out set of spark plugs in it, and replacing them with some nice e3's seemed to fix the issue.