If you mean that the engine cuts then coughs back to life and repeats this many times, then I experienced this phenonemon a few years ago. It was due to a corroded part of the idle cut off system in the carburettor.
It can also be caused by a mixture control not extending all the way out (or down in the PA28 Warrior's case). An overrich mixture can lead to a momentary surge of power after the mixture is put to the ICO position (hot temperatures caused by long periods on the ground after flight without sufficient airflow through the engine cowls).
May I also take the opportunity to point you to an engine troubleshooting website: <a href="http://www.aeas.com/proceed.htm" target="_blank">http://www.aeas.com/proceed.htm</a>
Kermie <img src="smile.gif" border="0">