GF's 20XE had been running - not badly, but just not quite right.
kangerooing, poor take off from standstill, lack of power etc etc.
did the usual checks as peeps from here suggested - no change.
Finally changed the AFM - even though it was OK as far as the ECU was concerned. Changed it for a very clean 60K mile version in a scrappy. now runs perfectly.
yeah - happy gf!