The grunfield is a strong opening against 1.d4
I think your getting your openings mixed up...
1.d4 Nf6 2. c4 g6 3. Nc3 d5 is a grunfeld.
1.d4 Nf6 2. Nf3 g6 3. e3 d5 is a colle system and not a grunfeld.
<Harry07> Agreed (well, atleast at my level =P)
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The grunfield is a strong opening against 1.d4