1NZ-FE service specs. + Spark Plugs and Torque Specs.
 

As you can see this is for a toyota yaris, but same engine as the 2005 scion xa.

Page 21 and 22 have spark plug and torque specs.

I was looking for quiet some time to find this info. I just thought it would help.

Back when I was a go-fur at a Chrysler dealer, the rule of thumb was to snug it down, then a quarter turn as the gasket seats.

Also it helps to do them hot to avoid breaking as some alloy heads can back the insert out.