Theres a couple things you need to do and check.

First, you need to try cleaning out your throttle body. Get some throttle body or carb cleaner, and a rag, and clean it out really good. Pay close attention to cleaning the throttle plate, top and bottom. Soak the rag and throttle body in cleaner, wrap the rag around a screwdriver, and clean deep inside.

If that doesnt fix the problem, unhook your throttle cable, and see if your throttle pedal sticks. If so, try lubing all the pivot points on the pedal.

If THAT doesnt work, feel the spring action on the throttle body for stickyness.

Could also be a vacuum leak. Thats a whole nother story on finding that. Look over your vacuum lines and check all your intake tubing for cracks. Spray starting fluid along any vacuum or intake line and see if your idle increases.

Could also be a faulty idle air control valve, but I doubt it.

You should be able to find your problem using one of these methods.

Finally, set your idle speed to ~750rpm by turning the screw located on top of the throttle body.