Hello, this is my first post here.

I'd like to start that I bought a 2008 used aveo last saturday for $7761 out the door with 34 thousand miles on it.

I read the manual, and noticed spark plugs need to be changed at 30000 miles (I think I read that right). The previous owner was a rental place and their definition of maintaining seemed to be oil changes only. I already swapped the air filter with a STP.

I hear a heavy low rumbling which is enough to seriously vibrate my steering wheel when the engine is idling in drive that goes away when I even tap it a little bit. That happened to my last car when I needed spark plugs changed out.

So here comes the question... I have a box of 4 ngk standard copper spark plugs sitting on my desk (that I can return), with some boot lubricant, and spark plug lubricant packages in my trunk.

Should I be using ngk standard coppers, and change out every 20k miles (which I have no significantly terrible objection to doing), or should I take a leap and go with iridiums.

I've seen lots of people complain on multiple forums about aveo problems with platinum, and problems with bosch, aswell as ngk copper vpower.

Which is better for power and fuel efficiency, stock coppers, or iridiums?
Thank you for any answers.