This is on a '74 2.0. This car's been on and off the back burner for a number of years. (To many cars). It now runs very well, "Except", when it's cold, it idles perfect. As it warms, (about 2 minutes) the idle gets faster to about 1800 rpm. After a 15-to-20-minute drive, I shut it off. Restart a few minutes later and the idle is slow to wont idle fast enough to keep running. So, I'm checking the Auxiliary air valve (I took it apart) and when it's cold, it's open halfway. When it gets warm, it closes. Shouldn't it be opening when warm to let in more air to keep the idle speed up? In other words, lean out the mixture? I would think, when cold, it should be closed to richen up the fuel and warm, open to lean out.
Am I 180 degrees off?
Thanks for any input.

The AAR closes when warm. When cold, it’s open.

Yeah. Sounds like it is working. These are notorious for poor warm start since the head cools faster than the sleaves. The car tries to run too rich on those situations (cht sensor). In this case, after 20 minutes the heads are probably much warmer than the sleaves/case! Mine tends to handle the warm restart pretty well, but that may be because I have mucked with it a ton.

its a designed vacuum leak, for higher idle when cold. Once the heated the valve is closed & should idle @ 800-1100

I second a vacuum leak. Do a smoke test, search YouTube on how to make a smoker for $10.

The aar is a controlled vacuum leak. A crummy low idle on a d-jet is not ever the result of an actual vacuum leak.

I am kinda leaning towards, no leaks, since I installed a new vacuum line kit on the engine and have gone through it multiple times. Also, when I pull the vacuum hose off the AAV, (creating a leak), engine idles at 2K.
I've replaced the CHT sensor twice, new MPS, replaced the, I believe it's called, ambient air temp sensor and all the normal things like ign. wires, plugs, cap, rotor, points and everything I could think of.
I wonder if poor valve adjustment could cause slow idle? Sometimes I imagine some clatter but then I think, no, that's a normal sound.
Thanks for all the replies. Now I know how the AAV works.

Did you read my posts? This is a known issue. It's normally just confusion on the part of the ECU. Messages from the sensors not matching reality. It happens to me (although not so badly I care) every time I run to Wegmans for something quick and then hop back in the car. It normally takes a minute or so of driving to get it happy again.

Start with basics- setting the timing and the valves correctly is important.
And just because you replaced the vacuum hoses doesn’t mean you don’t have a leak somewhere. Do you have all of the correct matching FI bits for your engine?
New MPS? Has it been calibrated for your engine?

Lots of possibilities that require methodical steps to troubleshoot, but that’s how you figure it out.

You can see more about how the AAR works in this video...forward to 7:15 for detailed shots.

https://www.youtube.com/watch?v=cBdjLrxvBIM

Have you removed, cleaned, and re-greased the advance plates in the distributor?

That dist. Plate cleaning and greasing is just a good idea all around.

Yes, I did read but confusing. So, heads cool, it runs rich, then heads warm, it runs lean. On my car, when warm, I can remove the hose from the AAV (to add more air) and idle picks up. I can use my thumb over the hose as an air valve to get the idle right. Even 20 minutes of driving wont "get it happy again".
A while back, I did all the timing check, valve adjustments. Two different CHT sensors. MPS is not calibrated but is new and matches car. I believe, all original FI on board. I even had it at a shop that claims they know 914's, to get it running better.
I did go through the dizzy some time back so I'm sure it's still good. I've only driven it about 50 miles in the past 5 years.
I'll go through the YT video and see if I can learn more. Might be a bit since we just had a storm here in Nor Cal and blew my fence down.
Thanks again for all the responses. I'll keep going on it...

Did it ever run correctly? If yes, what changed since then?

When you say "I remove the hose when warm" which hose? The one between the aar and the intake plenum? That should cause the rpm to shoot up.

Do you feel good about your basic setup? Do you still have the retard hooked up? Does your 74 have an advance? What is your base timing at?

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Yes, to the intake plenum. And yes, the idle shoots up to over 2K. Used my thumb as a valve to bring the idle down to where it should be. I do feel good about the set up since I've worked on it, on and off, for years. Even had it a shop that supposed to know 914's. New everything, except the AAR, but rebuilt. Retard as in vacuum line to dizzy? Yes. As I recall, there were two different sides to the dizzy to connect it and I believe it's on the correct side. Base timing. I just check a photo when I was checking timing and it's from 2019. I don't recall.
The car never ran perfect. Didn't run when I got it, now runs great as long as you don't count the idle issue. I will check timing again, once I get our fence rebuilt.
Here's some before and after of the journey with this car. I was also getting cars at auction and repairing for a number of years so that's why this one got put in the back yard for long stretches.
Thanks again for the input...

Click to view attachment Click to view attachment

Nice job! A big huzzah for getting another one back on the road.

what a beauty.

Here is my suspicion. Your aar is working perfectly, it's the timing/advance/retard/weights.

The AAR is covering up the idle issue on the cold engine. As the aar stops pumping the idle up the car is retarded too much and your idle is therefore too low. I would first try just disconnecting the retard (and plugging the hose of course) to see if that makes a difference at idle. If it moves to where it should be, and you are not a picky person, just leave it.

If you are a picky person, like me, I would want it working correctly so I would immediately start looking to the timing. If the timing is where it should be (let's say 8 at 900rpm is good enough) with the retard disconnected, then you probably just need to adjust your idle air screw and possibly the ECU idle richness knob.

be aware that some early 74 had retard and advance (I believe) on the TB (2 ports or one port on the tb). Be sure your retard (the port facing the back of the car) is hooked to the retard on the can (they will have both but on a late 74 the advance side should just be lying disconnected). That should only have vacuum at idle and rapidly losing vacuum with opening the throttle. The retard on the can is the port facing the dizzy I believe. If you have that retard port hooked to the advance side of the can you would probably have the reverse issue with a high idle so that isn't it. If you have sticky plates in the dizzy you could end up timing the car a little randomly and afterward when the retard pulls it might be retarding too much. Good reason to be certain about that base timing if you are using the retard 'feature'.

One other scenario concerning the distributor - your vacuum can could be leaking. Pull a little vac on it and see if it holds.

My brains getting old so I may have to print that reply out, when I work on it. I think it makes some sense about connecting the vacuum to the correct side (I have 2 ports) of the dizzy. I recall using Dave Darlings diagram when connecting the vacuum lines.
We're going out of town tomorrow so when we return (after fence is finished) I'll give it a go, again.
Thanks for the nice comments and replys.