Wifes Jeep won't idle

As said above IAC. This is a pretty common 4.0 Jeep complaint. If it otherwise has pretty good power I'd look there first. As for the fuel filter, if you cannot remember the last time you replaced it, get a new one! This should be an annual part just like plugs and an air filter. If the fuel filter was so plugged that the engine won't idle, you will be way down on power.