it could be a vacuum leak.but if not. its possible that your throttle position sensor is not within adjustment where it is mounted on the throttle body
i had a similar problem after rebuiling my engine.
if you look at the sensor you will see that its held in position with 2 screws,the sensor has two slots which the screws go through.
as a ballpark the screws should be in the middle of the slots.if not loosen the screws and rotate the sensor by hand to get them in the middle or there abouts.even move it a little bit around the middle setting to see if it drops the idle to normal
if that doesnt work you will need a volt meter to get an exact reading with the throttle at a closed position,this reading is different depending if its a 2 wheel drive or 4 wheel drive sensor,
try the above and see how get on,if you need more info how to set up the sensor with a volt meter let me know