Grunfeld player's reponse when c4 not played after d4?

At my fairly low rating level, for the longest time I didn't really have a prepared opening response to 1.d4 and would play1.... Nf6 and then just kind of wing it.  Then as I started to take chess more seriously, I found that I really liked the logic and positions of the Grunfeld and have adopted it with some success. 

I know this is really a noob question, but it seems that while at the higher levels players play 1.d4 Nf6. 2 c4 fairly frequently, in my games I would say I get 2.c4 less than 30% of the time.

What do Grunfeld players like to play against other lines like 2. Nf3, 2. Bf4, 2. Nc3, etc.? What may I like if I really like the Grunfeld? In looking at the data base, it seems like 2... c5 scores really well against these lines and is very thematic of the Grunfeld, but what system would I be playing if I took that line? Or instead, would Queen's Indian make more sense against these lines? FYI from what I've seen of the King's Indian I really do not like it.

Well now that I'm looking at it, it seems like the Queen's Indian starts after 2. c4 as well.

You would need to know the "Anti-Grunfeld" lines and study them in a book on the English Opening.

After 1.c4 Nf6, it depends on White's move order.

If 2.Nf3, then 2.g6 3.g3 Bg7 etc.

If 2.Nc3, then you must play 2...d5 now!  The moment White plays Nc3, you must play ...d5, like 1.c4 Nf6 2.Nf3 g6 3.Nc3 d5.

The reason for this is simple, and a popular idea that many English players execute.  Those that play it as a legitimate opening and not a cheap cop out system, like "I don't know what I'm doing and will blindly play 1.c4, 2.g3, 3.Bg2, 4.Nc3 and then open my eyes" (which by the way, 3.Bg2 is bad against 2...Nc6 due to 3...f5! - White should play Nc3 in response to ...Nc6 at any point), will usually play the English move order with intention of allowing the King's Indian Defense, but not the Nimzo-Indian or Grunfeld.

Here's how:

1.c4 Nf6 2.Nc3 and now:

2...e6 and now 3.e4 is the Mikenas-Flohr and 3.Nf3 Bb4 w/o d4 is just the plain old "Anti-Nimzo"

2...g6 3.e4! - This is why you must play 2...d5.  By playing 2...g6, the move 3.e4 has all intention of transposing to the King's Indian Defense after 3...d6 4.d4 Bg7, but by playing e4 before d4, you've avoided the Grunfeld.

The anti-Grunfeld runs 3.cxd5 Nxd5 4.e4 Nxc3 5.dxc3 where Black has nothing better than to trade Queens with 5...Qxd1+ 6.Kxd1 and the White King will go to c2 with an extremely positional, queenless game.

Thanks guys this is really helpful.

Thriller and Stevie... If the opponent is going to blindly play the London system and play 1. d4 Nf6 2. Bf4, do you continue to play 2... g6? Many of my opponents who play d4 are playing London system blindly and I note that in master games 2... c5 scores ridiciously well for black. Thoughts on this line even if it is not Grunfeld?

There is no refutation, but Black has easy equality in more ways than 1.

Black can play 2...e6, 3...d5, and 4...Bd6 with easy equality.  Black will fianchetto the Queens Bishop but hold back on c5.

Black can play a Kings indian setup with ...c5 (like Dembo recommends), ...Qe8 and ...e5 (like Gallagher recommends), or a double fianchetto with 2...g6, 3...Bg7, 4...O-O, 5...d6, 6...b6,  7...Bb7, 8...Nbd7, 9...Re8, and 10...e5 followed by a quick ...e4 like Lemos recommends.

The first would not fit well with you as after 2.Nf3, he could still play 3.c4 and now you played ...e6.  If you do 2...d5, he can do c4 with no Nc3.  Usually in the Grunfeld, you wait for Nc3 before d5.  So to cover both london move orders, I recommend you look at the other 3 and see which works best for you.  For me, it is the double fianchetto, but of course, I am a Kings indian player, not a Grunfeld player, so for you it may be different, like maybe the c5 stuff, a move frequently played in the Grunfeld (dembo is a Grunfeld player herself).