By "rough, shaking idle" do you mean the rpm is fluctuating? As in the rpm needle slightly moving up and down? Or do you mean the car vibrates? "Rough idle" means the rpm is fluctuating. If it's just vibrating, it is called, just vibrating

 

Okay, it is just vibrating then :o

 

That's what I thought :P it's gotta be engine mounts. A bit of vibration in R and D are normal. It'll never be as smooth as when in P and N.

 

Yeah but that is not the case though.
I have changed the engine mounts, and it didn't improve it even slightly. It actually seems slightly worse. Thinking the new mounts could be defective, I requested the warranty on it and got a new pair of mounts (yes I have 3 pairs of mounts at home now). It still didn't improve.
Side mirrors are shaking, it is so unpleasant I have to remove my elbow from the door rest when I stop to a red light, or shift to N.

And it wasn't like that when I bought the car, I wouldn't have bought the car with something like that. I didn't have to shift to N when at red light.

Before I changed my mounts, during a regular check up to Mazda they told me to change them. But I suppose because the car was shaking, not because they are damaged. The original mounts don't seem damaged, cracked, or leaking in any way.

I will go to a garage some time, and ask for a compression test maybe.

 

There isn't much that could be defective with the mounts to be honest... they're basically rubber baloons filled with oil. For them to fail means pretty visible cracks and goo everywhere.

Definitely needs an experience mechanic to look over it. If you open the hood, does the motor itself visibly shake?

 

They can fail without leaking. Almost all of the worn motor mounts I've seen didn't have leaks.