heavy vibration of engine on idle

Have you replaced the iridium spark plugs yet?

 

That is not helping your problem. Buy the correct iridium spark plugs, do not cheap out on this very important engine component. Only use the correct Denso plug as specified in the owner's manual, do not buy an incorrect iridium plug.

Eventually if you don't resolve the engine problem, you are going to turn to a dealer tech or other professional mechanic, and the first thing they will do is inspect the spark plugs, tell you the wrong plugs are installed, and install the correct plugs at a big markup in parts price and labor. So do that work yourself, now.

 

MSRP is $13.20 and this particular dealer sells the correct plugs for $9.90 plus shipping. Add some air/oil filters, windshield wiper refills, etc. to leverage the shipping charge.
2010 Toyota Prius Parts - AutoNation Toyota Gulf Freeway Parts

 

Yes, those plugs are not wonderful. Since you have an engine problem you need to rule out any possibilities, and this would be one. The correct plug is Denso, SC20HR11.

Also, buy a spark plug gap gauge so that you can check the gap of the newly purchased iridium spark plugs. The correct gap is 1.0 to 1.1 mm. I set the new plugs to the narrow side of that spec, 1.0 mm.

 

For my 2006 135k miles, I just replaced mine with NGK4996 LSR Irridium, (O'Reilly showed these as the OEM)
$9.19/ea We gapped them at the store.
Also cleaned out the MAV sensor and throttle body very well.
Feels like the idle is a bit high since the install. Any ideas? Hard to tell what the norm is because I’ve only had it for a little over 2 weeks.

 

Engine idle speed is computer controlled.

 

Maybe it’s running better/more like it should? Hard to tell because there’s no tachometer. Should probably give it a couple days. The throttlebody was pretty filthy, and who knows if and who cleaned it previously?

 

Still feels rough when the gas engine comes on and off sometimes, like the idle is too high or there's a dirty fuel filter, though I just read in another post that the fuel filter is in the gas tank, and can't be changed, so I guess I have to rule that out...
Maybe I should run a couple tanks of the pricier gas and or add some STP fuel treatment, etc?

 

The fuel filter can be changed, but it's not easy, best left for later.

 

Maybe it's something else....? When the gas engine comes on and off it should be smooth yes? Haven't changed the PCV valve, maybe worth a shot.

 

How are you determining the idle is too high? What's the car doing that's not right?

 

As I mentioned, the engine idle is rough when the gas engine kicks on and off, like it's running too high. I feel like it should be smoother.
I notice it more when I'm at a stop vs, when I'm driving and take my foot off the gas.

 

When the ICE is on at standstill, it usually runs higher than idle, around 1300 rpm, because it is still warming up. If it is warm, it will shut down. When you're driving it will go down to 900-1000 rpm no problem.