I noticed today that the spark plug closest to the firewall on the pass side is shaking all over the place. It is tight, but the wire seems to be shaking at idle. Any idea why it would be doing this? The others are fine.

 

i would say that the pocelan part is broken on it. it will need to be replaced. pull her out and see. or if it has the screw on tip it could also be loose.

 

Yeah,and it should be running bad because I don't see how that plug could be firing or at least making it to the ground electrode.