OK, ... here's what I have:
82 GSL bone stock.

Here's the problem:
Rough idle when coming to a stop. What I noticed is, when the engine is decelerating, the Coasting Valve opens up (air is sucked through the hole in the air cleaner connected to the large end of the coasting valve). The problem is, when it gets back to idle, the coasting valve doesn't "turn off". if I plug the hole with my finger, air stops getting sucked into the hose, and the idle returns to normal.

Is the coasting valve bad?

Is there something that "turns off" the coasting valve that may have gone bad? Or is the coasting vavle just not returning to off?

 

coasting valve should have a solenoid that turns it on and off - doublecheck that the lead that goes to it is plugged in. you might also be able to use an ohmmeter to check the resistance of the solenoid. Some books recommend using a jumper wire from the battery to the CV solenoid to check for an audible "click" when the solenoid engages.

I'm basing these things of my 73 RX-2 which had a coasting valve as well - some things may be the same or different for you . . .