AFM-(Air flow meter) ? Often the cause of the symptons you describe, can just be dirty , can usualy be cleaned with contact cleaner but often wont last long after cleaning , can usualy be found located in the air pipe running between the intake airbox and intake manifold.

Have a nosey around here http://gm.ws123.net/EN/ it's a fair cow to use and more handy than exact but better than nothing , well , nearly.