Help me understand vacuum test

Hi All,

First post! I recently bought a 2016 Tacoma SR5 2.7L 4WD with 70k mi with a good maintenance history.

It drives great overall, except the seat and the cab walls shake at idle in D or R like at a red light (idles around 550rpm). Sometimes it's bad and shakes my head and eyes and feels like someone is kicking my seat. It tends to get worse the longer I sit at a red light. I know there are tons of threads about this and there doesn't seem to be "one" solution for everyone.

I have cleaned the MAF and throttle body, replaced spark plugs, tried new exhaust hangers, cleaned battery terminals, checked grounds, and searched for vacuum leaks, all without improvement. It seems better after I've been driving it on the highway for a while and worse in lots of stop and go.

No CEL, no codes or pending codes, no misfires on scanner (but it feels like it's missing or imbalanced). Idle long term fuel trim is about -3%.

My question is: I did a vacuum test (hooked up my mighty vac to the intake manifold port for the brake booster hose). It showed a rapidly fluttering needle between 20.0-21.5 inch hg at idle in park.

Is this normal or abnormal? I believe my last truck had a steady needle with this same gauge. The exhaust sounds and feels like it's "sputtering" kind of like the vacuum gauge needle flickers.

I would appreciate knowing what you guys think and any suggestions you have!

https://youtube.com/shorts/751gE6O2KTY


Thanks
Matt