The throttle body is the cylindrical device at the end of the flexible air tube, bolted to the intake manifold, and is approximately four inches in diameter. Inside this is a round throttle plate that rotates to meter air into the intake manifold. The plate is rotated by the throttle cables, mounted on the large pulley above. Your problem is one of idle control. If this plate and its surrounds become dirty, air will not be metered properly and the idle will be off. So the immediate cure is to "clean the throttle body" (see FAQ Engine Performance section) and reinstall it. Then you should test the throttle position switch for proper function (see FAQ Engine Sensors). If those two check out, then take a look at your idle air control valve, beneath the intake manifold, and try cleaning that out (again, See FAQ). If that does not solve your problem, you should start looking for intake vacuum leaks in the air tube or the manifold gasket.