rough idle when warm

[rah575554eg]

Yesterday I noticed my 03 gtp was idling really bad after getting home from driving on the highway. I am thinking it might be the iac but not sure. Also I am getting horrible gas mileage in town around 11 MPG. I've replaced the fp, fpr and fuel filter no change. I'm am not getting a ses light either and noticed after changing the plugs that only two cylinders the plugs were really black. Bad injectors?

[Scottydoggs]

have you tried to clean the throttle body yet, that may help out, and a o2 sensor may be on its way out.