So I've been reading a lot on this forum for a while now I just got a 2001 LS430 Lexus last year given to me and it's been very well maintained. It's always been maintained at the dealership and only has two owners. The person who gave me this vehicle is my parents. They were just going to get rid of it and sell it but then I had a Toyota Celica issue and they decided to give me the lexus.
So here's the problems. I went out to do some errands, I had to go to the store and a couple other places and then home. As I was heading into town the flashing check engine light comes on with the VSC off light that comes on. As I was going up a hill there was some shakiness in the acceleration but the shakiness is not constant. It's around 2,000 RPM and then above 3,000 RPM and then at higher speeds, it was pretty shaky in the acceleration area. Not the tires, nothing like that. Everything such as rotors, tires and everything else, all that is good to go. So I did what I needed to do and came straight home to figure out what was going on. I did go to AutoZone and I plugged it in and no codes were popping up at all. Strange. So today I started her up with the engine Hood up, to see if I could find anything, possibly an air leak or anything like that, I didn't notice anything there. I did notice something different though, the radiator is full of fluid but the reservoir tank is bone dry. And there's a white crusty substance that's dried on the outside of the reservoir tank. Upon looking around the radiator, the radiator hose needs to be replaced because it's starting to weaken. But no leaks. But there's tons of air in the radiator system and so I don't know if that's related. But I was going to go ahead and put that in there anyways. All this happened out of nowhere yesterday. One thing I do remember is we have some pretty gnarly speed bumps in our shopping centers and our small mountain town, and I come around the corner and went over the speed bump, and it did hit underneath but I'm not sure what it did hit. Not sure if that could hurt the catalytic converter, and if that would trigger this issue as well, I'm just trying to stay everything that I have noticed. Another separate issue is my cabin filter it's completely jam-packed with leaves, dog hair, and just gunked up. Not sure if that can cause any issues since it's been like that for a while. As for the air filter under the hood, I took a peek and it looked okay, I'll look again in a better daylight. But I even watched the RPMs drop down to 200 RPM as well briefly when I started the car leaving the store. It ended up correcting itself. I don't think I seen it drop that low again. When I look back the last 2 months, to see if I noticed any thing and put it off, I did notice that I started feeling a very very light shaking well the car would sit at the stoplight. It was so light that I didn't think anything of it. I thought maybe it was just the heater or something or the air conditioner. But now that I think about it that shaking I think got worse and worse to this point. Any feedback will help thank you guys.

 

You have thrown a lot of problems together. "The radiator is full of fluid but the reservoir tank is bone dry": I have had a comparable issue for years. I lose coolant from overflow tank quickly (over weeks). Think it is leak in overflow hoses? Anyway my car never overheats and the radiator itself never loses fluid. Engine is perfect.

Cabin air filter seems irrelevant.

If your CEL is/was flashing, that is serious. You should have a mechanic check it out t avoid (worse) damage. Flashing = some serious misfire potentially, vs just a bad emissions reading.

 

By the time you hit the primary CATs you would have ripped the sump off the motor.
Since it happened after you went over a big bump, have you checked that you don't have any coolant in your Transmission fluid.
That bump could have busted the pipe in the bottom of the radiator and resulted in water in the ATF, which would explain the lumpy running.
What's the mileage? When was she last serviced?