my 4th move is normally 4.e3, thanks
QGD - Cambridge Springs Defense

someone may have already brought this up but in your 7. a3 Ne4 8. b4 line, cant you play Bxb4 axb4, Qxb4, and white will lose the knight on c3 and the two pawns...

I played QGD Cambridge Springs with much success, one of my favorite GM " Alekhine" played it against Capablanca to win the match.

It wouldn't surprise me if this reapears some day in high level match play.
How many stodgy old openings have shown up at the highest levels, especially during match play? They are being revisited with the question, "how bad can it really be to get a solid, equal position when playing black?"
I remember when the Petrov was considered so fossilized it wouldn't be touched by top level players. Kramnik decided that a solid defense to 1 e4 was probably a good thing after all. His record with it tells all. He drew something like 65 games, won 6 and loss 13. Not exactly thrilling results but when you're facing Kasparov, Anand or Carlsen from the black side you may not be so concerned about thrilling.
Personally I think the Cambridge Springs Defense has more going for it than the Petrov.
One can call it dull or lackluster but as Topfrox pointed out the Qa5 move isn't just a cheap shot at the Nc3. In addition to getting the queen out of the pin by the white bishop (Bg5), that bishop now looks sadly out of place and it can't get back to the queen side when the action starts over there.
In many variations black wins a pawn in exchange for the two B's and center pawns. But if the game drags on the extra pawn may tell. Here's one of the older variations which is as dynamically even today as it was when Lasker played it.
My age is telling but I remember when so many of the defenses used today were considered hopelessly dull and drawish.
They are dull and drawish lol.
well i remember the opening was very popular in the lasker era of chess...i think chess students of my generation were forced to be familiar with lasker. But maybe that changed.
I think the Lakser is trendy again but confess I don't follow it much. There are a number of d4 books that recommend the Exchange because it as viable, rich, asymmetrical and you can avoid reams of theory if you play it as White. So getting to the Lasker, Orthodox, Cambridge Springs and the like are difficult if White doesn't permit it.
Schiller wrote a monograph on the Cambridge Springs and evidently it was considered formidable back in the 20s and 30s to the point where top level players switched to the Exchange. So the Cambridge Springs disappeared from play back then until the Exchange was tamed somewhat.
Yuspov and Smyslov were respsonsible for resurecting it modern times. Kasparov won a world championship game against Anatoly Karpov with it. If there had been any question of its legitimacy that was likely a proof. Beating Karpov in the QGD back then was a quite the feat. Doing it with the black pieces was phenomenal.