If your stuck in the Serpent Temple trying to open those blasted doors, don't fret. It really isn't all that hard, it only took me around 10 minutes to figure out without wasting much serpent coins at all. If you kill a lot of Serpent followers then you should have plenty of coins.

First when you enter the doors room, from left to right I shall name the levers from 1 to 4. the 3rd lever on the right when pulled down, with all the other levers up and coin entered, opens the first door on the far left. in all the rooms spiders and snakes come out, so be careful. Then the first lever pulled down with the 3rd one still down opens the next door. Pull the first lever back up after and pull the second lever down, another doors opens. It goes in that order from what I found out. The last door in the middle of course has the chest with that missing last Monkey idol in it. Hope this helps anyone....