I have a weird noise coming from the large air hose that enters the air filter box from underneath. It's the one that's nearest to the oil filter side (beside the idle compensator I think). I've traced it to a large round valve? directly under the air box. What is this thing and why is it intermitantly creating a vacuum (no noise) then blowing air into the air filter box (very noisy).
Oh yeah, the car is an '83 12A carb fully stock. I'm suspicious that the cats may be clogging up. Time to hollow those out I guess.

 

That, my friend, is the hose to the infamous shutter valve. I just clamped mine off and now my rex idles WAY better. As far as I can tell that little device is one of those Mazda "Rube Goldberg'" thingys, very much like the 83 through 85 oil cooler tower. Clamp it or plug it up you'll be happy you did.