1997 Chevy Cavalier Car rocks while idle

Hello there,

My car SOMETIMES rocks very hard when it is idle or breaking to a stop sign/red light. It also has stalled on me one time.

My mechanic hooked it up to the computer, and it said it was a mis-fire. His advice, since I was trading in soon, was to let it go unless it stalled or got worse.

After I left there, the shaking stopped, only to return about half-way home. Then it stalled out. So here I am now.

My question is do you think it could be the spark-plugs? There is some water/oil/gas/some liquid I can see in the connection, is this bad? Should I try to dry them off? Get a new set? I know it could also be the coils behind the engine, but I can't fix that myself. So I'm hoping you guys can tell me it's the spark plugs. :P

Thanks in advance.