When the throttle pedal is twitching its the throttle body thats correcting. Its trying to stop the engine from cutting out, could be one of several problems, throttle body needs a clean and reset..first thing id try, cures most idle probs on lupos. Then id check breather system, vacuum pipes for leaks (your hunting issue) or if you have access to one, use a scantool or vagcom to see what codes you have, more than likely lambda or egr faults due to the throttle failing. Hope this is helpful. :-)