I'm sure this is a repost but I tried searching and gave up after several pages. My XJ started misfiring the other day so I changed the plugs and coil , and has since stopped misfiring. Now when I crank it up it idles pretty rough (it idles at 500 RPM, not sure if that's normal) and when I put it into reverse without giving it gas it dies. I'm going to pull the IAC tomorrow, inspect it, and clean/replace it. No check engine light or anything. Does anyone have any suggestions on what could be causing this?