I have a '03 Lincoln navigator that idles real rough won't go past 3,000 RPMs.
Do you have any warning lights on the instrument panel? Did you try running a diagnostic scan?
Follow this troubleshooting chart:
That thing is over two decades old and there are many things which can cause those kind of problems. Please provide all information requested in the posting instructions located near the top of the page, as well as troubleshooting steps taken so far. Thank you.

I have a '03 Lincoln navigator that idles real rough won't go past 3,000 RPMs.
Are you in park when you're trying to revv your engine? Some premium cars from that era started revv limiting when in Park to cut down on "neutral drops", basically you rev your engine almost to red line and throw it in gear at the same time. It ruins your transmission.