1996 Volkswagen Golf the car engine idle is not consistent

On start-up the car generally runs good the problem occurs when ever it wants to. The car could just be warming up and start reving the engine then backing off repeatedly for up to a few minutes; this has also occured while driving the car a low speeds. The throttle body is controlling the movements in engine speed, (i can watch the butterfly valve opening and closing with the corrisponding engine speed). Is there something wrong with the throttle body or is the problem something else controlling the input signal to the throttle body. Just to let you know I have changed out all of the intakes vacuum lines.