Well, since you said almost nothing that would help anyone even get started all you're going to be able to get are wild guesses all over the map.
Give it a new set of plugs and wires. Is this distributor based or a coil pack? Give it new fuel and air filters. Clean out your throttle body. Check the fuel pressure - under load. Put a vacuum gauge on it and check for evidence of exhaust blockage. Is the check engine light on? Is this a manual or automatic? Howe many miles are on it? Are you actually saying that it routinely idles at 1500 rpm? Too high. Look for vacuum leaks & pay special attention to the MAP sensor & its connection @ the manifold.