Ok now I know this is going to sound like a stupid question, I'm going to change my water pump which means I will be changing my timing belt as well, but which one of these circled Items should I change? I keep finding the Idler Pully but not the tensioner

 

you change the tensioner ( box on the left ) the other box is the hydrolic tensioner and you just reuse that.

 

Do you know where I can get one? I check the local part stores and all they have is the pulley, lexus/toyota is all out.

 

You dont need to change neither.Jut change the belt and the water pump,its not required to be changed,unless you have damaged it.

 

you dont need to but you should atleast change the bearing. if you dont change it then over time it could start to make noise and you will have to do it all over again.

 

Thats what I was thinking, but do you know how long the tensioner lasts for?

 

it will vary on every engine depending on enviroment. hot cold, dusty, sandy it can last years and years or only last a few its really hard to say. they usaly run about 20-30 id assume so why not just change it? if your car has 172xxx miles on it and its never been changed id just do it. its more or less a maintenance thing