Running Rich?
 

Car seems to be running a little rich. It misfires a little at idle, is heavier than normal on gas, and even after long runs, the exhaust is extremely black and sooty. Other than that, car runs very well.

Friend of mine said it could be plugs or maybe the O2 sensor. I'm going to drop it by the dealership this week, but I want to make sure to have them check everything it could be. You guys have any ideas of something else I should bring up that might cause this?

Thanks!

well, I think it's probably your Ignition Coils, or at least one... but it could be your cat or spark plugs...

If I am you, I would take it to the dealer, explain to them all the symptoms you've been having and wait for their professional expertise. If you tell them what you think it is, you might fool them into looking into a totally different direction. So, just wait for their answer.

I hope you fix the problem soon...

check your connection from the coil to the spark plugs, make sure everything is fine and dandy first, and make sure your wires are good