2004 Jeep Liberty Idling

The idle is computer controlled, so there are no adjustments. Check for leaks in the vacuum system, Ckeck you vac hoses, look for a hose that is dissconnected, cracked or collapsed. A leaking intake can also cause a fast idle. Is your check engine light on?

Knowing what fault code has turned on your check engine light will give you the place to start diagnosis once you've done the "quick checks" (visual check for faults like hoses and visual cracks or leaks in the intake) There is a standardized diagnostic flow chart for each fault code, your mechanic most likely has or has access to these.
If you have some mechanical knowlege and you feel conifdent about doing it, you can check the intake for leaks. This is done by filling a clean spray bottle (if it is a used bottle, I don't recommend using one that contained anything flamible, just to be safe) with water, starting the engine and spraying the water around the intake. If there is a small crack in the intake or leak in the gasket the water will momentarily fill the gap and the idle will reduce when the water is sprayed on the leak.
Let me know what you do.