I am in the Yuan Ti dungeon in Chult and have finished wiping out all the monsters I can find, yet there appears to be more rooms in the South West portion of the dungeon that I cannot find a door to. Am I wrong or did I miss something?

Yeah, I am pretty sure that you have missed something. Go back and double check all of the walls for doors, or a hidden door. I can't remember if there is a hidden door or not.

I went back and tried putting on initiates robes,searching for traps, putting skulls and hearts in the dragon chest in the room with the bridge, and pulled all the levers i can find but I still get nada. I'm about ready to say hell with it and move on, it only looks like 3 or 4 rooms. I have a save there if I find out there's anything good. Thanks for the help anyway.

Before you give up, are there any levers or buttons to push? That is all of the advice I can give. :(

I think I know the room you are referring to. It just opened by itself for me, I never had to do anything. From memory, you will have to take care of all foes in that dungeon before Iselore gives you the next assignment. Dont forget the missing temple pillar so you can summon the guardian.

There's a room with a puzzle lock. It has bricks protruding from the wall and floor that you have to press in a certain order. It's not a hard puzzle. I figured it out in only a couple of tries.

The southwest part of the Yuan-ti lair is where the coiled cabal and vipers fang assassins have their lair if I remember correctly. The hallway to the west of the entry stairs leads you straight (if you follow it without entering any of the rooms) to the room outside the coiled cabal rooms. The room before the cabal contains a fire bath trap (similar to the acid bath right beside the entry stairs). If I remember correctly there are only 2 rooms of the main room with the Sorcerers and the Assassins.

If you had choosen the stealth approach you could have tricked an assassin and a sorcerer to reveal info for xp. The assassin tells you the first 3 blocks to press to open the treasure room door (the cook can tell you the last 3 once you get the 1st 3 from the viper's fang) and the socerer can tell you about summoning the guardian. Never fear if you did not take the stealth approach to start, you only missed 1200 xp each for getting the info.

One tip for fighting all the sorcerers and assassins, stay in the room with the fire bath trap (after deactivating it of course) and use the doorway to the cabals area as a choke point. There are a lot of assassins with a lot of +2 arrows and it is much easier to keep the slowly filtering into your room rather than having them surround you in their rooms. Plus the sorcerers cast quite a few spells...