Revs dropping randomly at idle, car jerks

As a disclaimer, the car's an 04 Hyundai Elantra GLS sedan with the 2.0L 4-cylinder.

So, sometimes when I'm stopped, and the car's in either drive, park, or reverse (never happens in neutral that I can tell, or above 10mph), there'll be that little jerk that feels like someone just kicked the back of your car. The wheels don't move, but it feels like the body moves forward about an inch and then comes back. Whenever this happens, the revs drop between 100 and 250, and the strength of the jolt, for lack of a better word, is directly related to how much the revs drop. The car idles around 700 normally, but has dropped as far as 400 when this has happened. My guess is that the car's stalling, but I can't figure out why. If it was the transmission slipping, it'd happen in the other gears, right? All my fluids are fine, including transmission fluid. It can't be a spark plug, or it would be happening constantly instead of just once in a while. I wouldn't think it's the throttle position sensor, as acceleration is smooth and it doesn't do it while just coasting with my foot off the gas. If I had to guess, it's something with either a spark plug wire or one of the coil packs that the spark plug wires connect to. I just bought a new set of wires, so I'll probably install them in the next couple days and I'll try to remember to update this with whether or not that fixes the problem. The only other thing that comes to mind is the evap canister - it could need replacing, so I'll also detach the sensor for that and see if that's the cause, assuming the new wires don't solve it.

But anyways, I was just curious if anyone has had a problem like this. The car's got a tad over 78k miles on it, and I've never had anything need done outside of regular maintenance.