So where did I leave off? Ahh yes the water lines. You see on this 1UZ-FE engine they routed some simple water lines that go from one side of the rear water bridge all around the engine and then back into the other side of the water bridge. It's that simple. The coolant isn't necessarily pushed through these lines by a pump but the flow of the whole system just circulates it nonetheless.
The rear waterbridge between both banks of cylinders. Two large nipples for the heater core and two small ones that make the lap around the intake manifold for emissions controls.
I'll just start from left to right with the flow of this water circuit. The water goes from the rear water bridge to the EGR and smog air outlet on the intake manifold. It merely passes through the air outlet as to bring it up to temperature quicker. By design all of the EGR system is brought up to operating temp as fast as possible to be effective as quickly as possible. So the coolant goes through the U.S. spec intake manifold EGR passageway and then on to the Idle Speed Control Valve or ISCV. This is so that the ISCV is warmed up quickly so that the engine runs properly as quickly as possible. If you happen to leave the hood up in a blizzard this would also help thaw out the ISCV upon firing up the engine.
Here is the Idle Speed Control Valve - and the 3 obvious water lines:
Then the coolant goes to the throttle body for much of the same reasons that I just listed for the ISCV. The biggest problem I have with this whole route for the coolant is that the throttle body is heated up to be much warmer than we want. Of course we want the air going into the engine to be as cool as possible to we will not be allowing coolant to complete this circuit. It would normally go through the throttle body and then complete it's journey to the left side of the rear water bridge.
Of the two coolant nipples exiting the water bridge I blocked off the one on the left of the engine. The one of the right I will connect with a coolant line that will go to the ISCV and then to the front water neck. Oh did I mention that there is also a short water coolant line from the front water neck (that contains the thermostat) to the ISCV? So that will work perfect. I don't mind running coolant to the ISCV. I want my idle working perfectly so if the engineers at Lexus decided that it would be good to preheat the ISCV then I'm on their side on this one. Maybe it works better when it's warm.

That also makes it easy on me. Blocking off the rear water bridge hose connections is a pain in the butt. I tapped and drilled the left side one but I would rather not do this to both of them. What happens when I put a Turbo on my engine and I need a coolant line?

So I'll leave the right side one alone and hook it to the ISCV and then have it exit to the water neck. This also makes it easier at the front of the engine since I only have to block one of the coolant lines on the ISCV - instead of 3. I'll put a bolt in the one I want to block off and then weld it in there carefully. Ok that's all done.