I'm just wondering if when i eventually buy it, all the dlc will be there if i actually buy the pass but have not played the game.

I've been asking myself the same question, and so far, it's a yes.

Yea, I've been looking to get LA Noire, but I liked to finish Fallout 3 right now. Looks like I be grabbing the pass soon then.

I'd recommend getting the Rockstar pass. Even though I have one of the DLCs from just purchasing the game (Naked City), it's still more financially beneficial for me to just get the pass rather than download things separately.
 
i.e. Four total DLCs (Naked City, Reefer Madness, Slip of the Tongue, and Nicholson Electroplating) for 320 MSP or 4 dollars each. 
Rockstar pass offers all of the above plus more for 800 MSP or ten dollars.
Even if you have one of the DLCs from buying the game, you still have to download all of them (assuming you want to 100% the game and experience the entirety of it) for  at least 12 dollars (assuming you don't want the rest of the benefits). 
 
Also... I see no reason why none of  it should be there even if you don't own the game right now. If all else fails, there is always the re-download option.
 
Overall, I think just buying the pass is probably best :) Neither should be going anywhere.

The Rockstar pass will go up in price by $2 in a couple of weeks, so if you're definitely getting the game soon it makes sense to buy it now. However, be aware that you can't download the DLC until you have the game. The Rockstar Pass isn't all of the DLC packed into one file, it just unlocks the content in a download menu in the game. You have to go into the game and download the DLC from there.
 
If your goal is to have all of the DLC integrated into the story you should be fine if you download it as soon as you get put in the disc. There's only one piece of DLC that takes place in the first half of the game, it's only ~250 MB, and it will take a couple of hours to get to it.

If you plan on getting L.A. Noire, definitely pick it up now while it's cheaper. Some really awesome content they're giving away with it that would cost you some extra dough, if you bought them all one at a time.