Serious Rattle and Shake *not at startup

Just the other day I was going to take a nice long drive and the Prius acted a little funny. The battery was down to two bars and when I started the car it was fine, took it up a small hill and it kind of slowed the motor, shook like crazy and then revved pretty high two times... I shut it down... Convinced the battery just needed charging I tried to drive around a little bit, but my copilot wanted nothing with taking the Prius at that point. Yesterday, days later, I returned. Took the Prius for a short drive this morning and the battery went back up to darn near full on the dash. Thought things were back to normal.

Just now, at lunch, I took a short drive, maybe 3 miles. Everything seemed fine. Went to make a K turn to park the car and again, the motor kind of started to shake and rattle at what felt like a low idle... parked the car... Later I drove home, things at first seemed OK. Went down that small hill to my house and was going to parallel park... Battery was not low... probably two bars off full.

When I stopped to back up the motor came on and it started to shake... switched to reverse and there was some crazy shaking... Shut the car off. I started again and using the battery pulled into the driveway.

No check engine light.
No loss of coolant or any issues at first start.
MPG on that short trip was around 50
No strange smells
No work done prior to this
Slow burner of oil but level is fine
ODO at around 205000
EGR cooler pressure washed late 2024, EGR piping cleaned
For the past few weeks I had heard intermittent rattles ( not shaking ) that I assumed was a heat shield

Any thoughts?

Appreciate the help

 

Added that info above.. thanks. I did take the EGR valve apart ( shouldn't have done that) to clean it and was careful to put it back together. Zero problems over 15K miles later

 

I always thought the shaking was at startup when coolant is in the cylinders. This happens after a little driving. Doesn’t seem like hydro lock

I did clean the intake manifold but the must admit that the inners were located with a substance like tar so cleaning that was a chore. That said I soaked and soaked and sprayed. Was at it for a week with degreasers and boiling water…

plugs may not be newer. I would expect mpg to have issues and drivability other than idle??

pretty sure I cleaned out the throttle body when I was cleaning the intake manifold, recent air cleaner.

have not touched the fuel injectors