1999 Oldsmobile Alero Idles rough and not on all cylinders

Hello, I am working on a 1999 olds alero with the 2.4L in it (quad 4 engine). It doesnt run on all 4 cylinders. Ive never worked on one of these engines before. Im not even sure how to tell which cylinders are not firing or if the cause is fuel or fire. I pulled the plugs and they all look light tan. So none of the plugs are black or have signs of not firing, as far as I can tell, so that doesnt help. No check engine light noted. Autozone or advanced auto can test the ignition modules but I dont know how much stock I would put in that. The car has 83,000 miles on it. I checked to see it has coolant in it and it does have the dex cool red crap in it. Tail pipe finger test produced typicial black soot on the finger. Im not sure what a blown head gasket would look like on plugs with dex cool coolant.