[djimellis]

On my 87 the valve is located on the drivers side down in the right hand corner of the block. The other valve, I only have 2, is to the left & up, at the right end of the exhaust manifold. This valve controls the flow to my hot water tank. As for why your is warmer on idle then at speed I cannot think of what that might be. I removed my heater core, motors, vent tubes etc, to install a new floor in the compartment. It was not a difficult job but you have to have a bit of time on your hands. If you crawl under the front passenger side compartment you can see if the air intake ports are open or closed & you should be able to hear the pump working the therefore put your hand on the output hose to see if it is hot.  Good luck.