Yesterday when I was driving, I started hearing some strange noises under the hood along with a vibration. So, I pulled over and popped the hood with the car still running.

It was pretty obvious what the issue was when I looked. The crank pulley was wobbling all over the place, I was pretty sure it was about to fly off so I ran and shut the car off. I was sure I had lost the bolt, but no, it was still there. Yanked around on the pulley, no play.... Ok that's weird I thought to myself.

Decided to start it again, and it wasn't really wobbling much. Revved it up. Now the wobble is completely gone.
I drove it around and it seemed fine... but I'm still worried.

What would cause that to happen? Motor is a D15b8.

 

Damaged crank, damaged crank pulley bolt, damaged cotter pin, damaged bearing(s), take your pick.

 

Cotter pin? You mean woodruff key?

 

That's the one.

 

Hopefully it's just the key!

It's just weird how it randomly started and stopped.

 

Similar problem on my 97 HX at one time. Crank pulley ended up coming apart and screwed up the crank threads a bit. Take a look at your crank pulley closely and see if the rubber is separating from the metal.