I have not seen any problems with my 2.4L 2009 Vibe spark plugs or coils. I doubt that the coils or spark plugs are causing your slow idle problem. If there is a misfire, the computer would though a code and your "Check Engine" light would be on.
If it was my car, I would start by cleaning the throttle body. Check this video for the basic steps of cleaning: https://www.youtube.com/watch?v=pnrAMZlkSSA
As noted in the video, do not push or move the butterfly in the throttle bore by hand as it will damage the throttle body. Use throttle body cleaner and brush and clean rags.
Next, pull and re-seat electrical connection on the throttle body checking for corrosion.
Next, clean MAP sensor with MAP sensor cleaner only. Do not touch the wire in the sensor. You will have this out of the car when you pull the air tube out and it is shown in the video too. Check that connection also.
Replace the PCV valve. If that sticks, it could cause idle problems and the valve should be changed as regular maintenance anyways. The valve is screwed in on the back, passenger side, of the valve cover.
Make sure you do not have any air leaks on the intake air feed tube and that the top of the air box is sealed to the air filter. I know mine can be a bit of a pain to get it back in properly and if you don't, you'll get a dirty MAP and throttle body again. At least that is what I would do to start to eliminate possible sources of idle problems making sure those things are in good shape.
And this video on why you should not move the throttle plate by hand: https://www.youtube.com/watch?v=JPNnHU6PYbo
Don't leave the throttle pedal floored with the key on for more than needed to get the cleaning done. Clean as much as possible with the plate shut before opening the throttle plate to clean behind it. A better break down of what is in the throttle body: https://www.youtube.com/watch?v=6-2Ui1PXQPc