Hi all - ‘84 GS, 12A…stock everything. Been working on the car quite a bit over the past year trying to get it to run adequately enough to drive around. Last year rebuilt the carb which solved one issue (flooding). Most recently replaced the intake manifold gasket/ O rings and the shutter valve. I think I’m getting there but can’t get it to idle below 1100 RPM no matter how much I back out the throttle adjust screw. My question though is this: when revving the engine I noticed a steady blast of air coming out of the ~1” dia rubber tube that connects the #1 A.A. Valve to the air cleaner housing. Is that supposed to happen?

 

The aav1 works on deceleration. The fsm has a test for that and all the smog valves. Sounds like one of the vacuum diaphragms is bad. If u don't have to smog the car u can just block it off. Ditch the air pump too. I had issues with them causing my car to fail smog. Inside the valve looked fine. But I would fail on deceleration. Your problem sounds like complete failure of the vacuum diaphragm.

 

Hey thanks for the advice! I’d prefer to keep it stock if possible but I don’t know if that valve can even be bought anymore. I’m guessing that if it’s totally failed it may be contributing to the high idle if it’s leaking vacuum. I’ll try that test that’s in the FSM.

 

N201-13-750 is NLA. it is the same 81-85 though

 

Roger that - thanks much for checking. I plan to study up on what I need to plug up to ensure that valve can’t leak vacuum. I don’t know if it’s a PITA to replace but even if it’s not, I figure a used one wouldn’t have much life left in it…

 

Remove the air pump aav 1 and 2. Block off plates you can get from Atkins mazdatrix racing beat and few other places.

 

Thanks - I’m going to look into that option! According to the FSM it seems that air should actually blow out of that pipe that connects to the air cleaner when engine RPM increases from idle. I am suspicious though that the AAV1 valve, air control valve, and/or the AAV2 is leaking air into the engine when it shouldn’t….

 

basically when the shutter valve closes, one (or both) of these things are supposed to open. its like deceleration fuel cut, but with a carb and mechanical stuff.
i had one where the air pump had come apart, and the pieces had jammed the valves open, so it acted like a huge vacuum leak, but it was really hard to find because it wasn't to the outside of the engine

we also might clarify that the parts catalog is calling the 13-750A the AAV #1, there is another valve in the air control valve

 

I appreciate that diagram- thanks! I just replaced the shutter valve and figure I’ll leave that alone. I’m thinking that I should be ok taking out both AAVs and air control valve and air pump and blocking off the resulting opening in the manifold. Anyone know if doing this damages the cat converter? I recall an air line running to it…

 

yes, cat needs to go if the ACV and air pump are removed.

 

Roger that - thanks

 

My plan at this point is to pull the AAVs and air control valve, block off the resulting hole, and see if that solves the problem I’m having. Two questions:
- can the air control valve assy be removed without having to remove the carb?
- since this will prevent air supply to the cat (and seems will kill the cat eventually) would the cat failure cause excessive back pressure and/or dangerous exhaust system overheating? In case it matters it’s not the OEM cat…I replaced it a couple decades ago with a Bonez cat/exhaust system
thanks!

 

yes, the ACV just unbolts from the side. if i'm trying to diagnose stuff, i'll drink a soda and make a gasket with no holes out of the can and see what it does.

usually the cats fail in these by breaking up, when you pull the exhaust the cat is just hollow

 

Thanks very much j9fd3s. I like your soda can idea. After I get the chance to do that I’ll report back!

 

I removed the Air control and AAV valves and temporarily sealed the holes left in the intake manifold. Problem persists although I think it’s running a little better. By adjusting idle mix screw & idle speed screw could get idle to 900 RPM, but not totally reliably and when trying to accelerate throttle, engine would bog down before speeding up, or just die. Couldn’t seem to find any vacuum leaks (with carb spray). The coasting valve failed the test described in the FSM though. It’s new… replaced it a few weeks ago as part of the effort to get things running right. I wonder if the shutter valve is sticking? At this point I’m not really inclined to reinstall the AAV/ACV, and am thinking of junking the shutter valve as well. I’m beginning to understand why so many strip their Nikkis!

 

its tricky to get all that stuff working, and then working at the right times

 

Are you certain you capped the nipple on the intake manifold which takes the large hose from the AAV#2? I spent a lot of time tracking down issues that are extremely similar to what you describe and I'm pretty sure my problem was either a bad AAV#2, or leaks from that hose. On mine the hose itself seems in fine condition (as far as holes in it), but the end that plugs into the intake seems to have not aged well (presumably because of the heat at that end). Anyway, just thought I'd mention that as a possible thing to check.

You also mentioned maybe the shutter valve was sticking -- I had an issue where I placed clamps on the vacuum lines running into the plate under the carb and one of those clamps was impeding the motion of the shutter valve actuating rod. Again, resulted in similar symptoms.

I just noticed you're in Maryland -- what part? I'm near Ellicott City.
Good luck getting this tracked down, I know from experience that it can be frustrating as hell...

 

aka, the mystery hose, 13756 in the picture

 

Thanks guys for the feedback. Kizmit99 nope not far at all from you! (I’m in Catonsville). I think I know the hose you’re talking about. …I’ll take a look but I’m pretty sure I plugged it up. Of course I may have plugged the hose but maybe the hose is cracked or otherwise leaking. And I’ll take a look at the shutter valve linkage. Maybe it’s sticking somehow.

 

This will likely be my last post on this thread, since I think I’ve concluded that the AAV valves are not the cause of the idle problem I’m having. Nor is the shutter/coasting valves as best as I’ve been able to determine. I’ll do some more research here and maybe start another thread. Thanks!