For an update, I changed all the injectors with new ones and it still has an engine vibration. I must have something bad in the valvetrain.

 

Hmm... Maybe a bad clutch, flywheel. Or a torn pilot bearing/bushing.
I have a vibration, too, I can feel it when my clutch grabs. I'll change the whole fw/clutch/pilot brg assy.
Good luck!

 

Remove the your serpentine belt and check your balancer, if it rotates on they pulley then it is bad. We have already broken 2. Cause mucho bad vibes.

 

It is kind of hard, so I turned off my fuel pump and turned the diz by hand to listen to each one, with only one plugged in at a time. This was on a car that is of course easier to do this on, as opposed to the Opti setup. You can also feel them when they fire, on a big honkin V8 though yes its more difficult.

Unplugging each one for a couple seconds to see if there is a change or no change sounds like a pretty good thing to try.