Vehicle vibrates at 650 rpm

I drive a 05 Toyota Hilux Surf with the 2.7L 2TR-FE, I noticed for a while that once the vehicle is warm up, idling around 750rpm in drive while stopped it would drop to 650rpm and make a vibration noise, the engine would vibrate as well for a bit and jump back to 750rpm with no vibrations, at one point when I had a catch can install to the pcv it was louder with it on when it drops to 650rpm, I clean my throttle body, maf, spark plug change and change the air filter not to long ago. I tried to find any vacuum leaks and can't seem to figure out where to look first. Back in January I had the coolant bypass pipe replace. Any ideas?

 

A while back I noticed minor vibration when the AC comes on and off during idle, which is around that 600-750rpm range. When you have this happen, are you running your AC or is it completely off?

In regards to my vibration, it was essentially quite normal.

 

How do you like the 4th gen with the 2.7?

 

Even my V6 Tacoma when parked and idling around 750rpm (AC off) has some sort of a harmonic frequency quirk. You can feel undulations in the chassis and it makes me queasy. Could be a related issue.

 

It makes the vibration with the a/c on/off and the climate control off

 

It's interesting that's for sure, it's not quick but get's me to where I need to go, it's not for everyone but I like it, I was looking to get the 3.0L diesel version but hard to find one with low km's and condition

 

This is while idling in drive, the engine would shake when I check while it was happening, anything that I should take a looked