Hmm did not say anything on the container about having to remove immediately after running for a set amount of time in the oil, I believe its only like a cap full you put in there or 1 oz. Not a huge amount. Any ways, I got really good gas milage on my last tank around 344 when I am usually getting 300-320. This was a couple of tanks after the sea foam. So it seems the things I did helped. But not with the vibration. I think it has to do with the tranny.
Leaving work the other day I was at a light, the car was still cold and it was doing the vibration at the light which I will usually shift it to neutral, and it will go away, this time you could tell after shifting to neutral the vibration slowly went away not immediately like it usually does

 

If you didn't add 1 ounce per gallon of fuel for a full tank and run that tank down to just below 1/4 tank you won't see the benefits of Seafoam.

 

im almost certain its your v-belt, or any other belt thats too tight or maybe stretched under the hood. ive been tweaking my belts here and there and the vibrations come and go, a week or two smooth, then a week rough. i doubt its your Tranny tho cuz u sound like you have the exact same problem as me and my cause definitely inst the Tran. besides, Toyota put together a fairly strong reliable tranny and with only 76k that definitely wouldn't be the problem unless you drive hard or haven't kept up on scheduled maintenance.

 

How did you come to the conclusion that your trans is causing it? Do you have shifting problems.

Some vibration is from normal wear of the engine mounts, without looking at it myself i honestly could not tell you what it could or could not be.

If you feel it is a problem then take it to a shop you trust.

 

im having the same thing with my tC, its an auto 06 with 57k. It vibrates when im stopped, but i put it in neutral and it stops, if i turn the AC on it starts, turn the AC off and it stops, I changed the plugs but i am afraid to seafoam my engine, mine could be motor mounts i hit a puddle of water really hard and messed my bumper/hydrolocked, but it was already doing it beforehand.

 

A/c compressor engaging is going to do that, you are placing a pyhsical and an increased electrical demand on the car when the compressor engages. If if was engine mounts or an engine running conditon it would do it regardless. You should really start your own post.

 

i wasnt trying to threadjack i was just saying im having the exact same problems the op is having.