Shudder at Low Speed, No OBD Codes

2015 Toyota Prius
156,000 miles
Regular oil changes and tire rotations
Trans fluid replaced about 20,000 miles ago
Spark plugs replaced about 20,000 miles ago

Hey everybody. My Prius has a strange shudder which shows up intermittently. When it happens, it feels like I'm driving over a rippled road. At first, I actually thought it was just ripples in the road, but I noticed that it happens even when I'm going really slow (too slow for it to be the road / tires). It has a sort of electronic, pulsating feel to it, like the car is throttling up and down rapidly.

This doesn't happen at high speeds as far as I can tell, and I don't think it's the ICE since my RPMs are smooth at all speeds. I get no diagnostic codes with a CAN-OBD-II scanner.

I've already read the other posts on this forum about shuddering / EGR / engine mounts, etc., but they all feel so similar and were all so inconclusive that I'm really confused about what is actually going on with my car. I can't rule any of them out without some good advice from someone with experience.

Any help would be incredibly appreciated.

 

This is almost certainly not a tire problem because it happens when I'm idling. More often, it happens when I'm rolling slowly into or out of a parking space; the oscillation is much faster than the speed the tires are turning at.

 

I haven't cleaned the throttle body, but I replaced the spark plugs about 20k-25k miles ago and I get regular oil changes. I replace the air filter every few oil changes when it looks bad, but I don't remember the most recent date. This problem seems to happen more on days when it's been running a lot. It doesn't do it from a cold start.