Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
There's several different things that could cause a high idle... Have you done any testing yet? Stored trouble codes?
This is the 3.0L engine, correct? Those are MAF systems, which tends to rule out vacuum leaks as a cause for high idle. Looking at scan data during the high idle would be the next best step, if possible.
Could be a bad idle air control valve (iacv).
When these go bad it will compromise your idle. Also check the accelerator cable if it gets hung up or moved from the holder it will give you problems. Lastly I would check your throttle position sensor some are adjustable to raise or lower the idle. Check out the youtube video on adjustment.