iodoform,

Go to
http://www.chem.ucalgary.ca/courses/351/Carey/Ch18/ch18-3-2b.html

It just explains the iodoform reaction.
Now to answer ur question,

in that site,
in step 4,
CI₃^-
comes out as a nucleophile,
but in case of ethanoyl chloride, there is a more electronegative Cl atom instead of Ph. hence it comes ou and not CI₃^-.

therefore iodoform comes out

|||^ly in ethanamide NH₂^- comes out