Some help with rough idle, please

My Altima is idling very rough. I changed plugs, cap, rotor, and wires but it persist. Before changing the wires the guy at Autozone pulled the code P0304 so he indicated misfire on #4, thus I changed the wires but same problem. I know it's getting spark to #4 all the way to the plug but this makes no difference in how the car runs. In other words I can pull the wire but the car runs the same. I suspect the injector but don't have a meter or enough tools to check with me ATT. Has anyone seen this problem before? Is the injector just held in place with the two philips head screws? Would it give a misfire code if the injector were getting energized but not operating? Thanks.

You should be able to hear the injector 'clicking' when the engine is running. The book says that you can try putting a screwdriver on top of the injector and put your ear to the screwdriver handle. Kinda like listening to a train on a train track.
The injector is actually under the cover with the two phillips heads. It should pop out because it is sealed by an O-ring.

mikepw, Thanks for your reply. I did as prescribed and it seems to be clicking. I also cleared the codes because I was afraid that what was stored was due to my troubleshooting. After clearing the codes, it still idles rough but the "check engine" light doesn't come on (at least not yet). Maybe the next code stored will be real. So I might be mislead on the misfire. Any general suggestions on rough idle in the abcense of a code? Thanks Again, sbb

Have you checked your timing? Also, go ahead and pull the #4 plug and check it's condition in relation to maybe the #1-3 plugs.

You could swap out the fuel injector from another cylinder and see if the problem moves. Release the fuel pressure by removing the fuel pump fuse and cranking the engine for a couple of second beforehand.

Your problem could also be an intake manifold air leak around the cylinder too so check it closely.

Thanks to both of you for the help. Have some work to do and will update on my findings.