How does auxillary air regulator work?

[shorepig]

I have an 85' automatic westy and I'm trying to figure old a bad idle during cold starts / rough idling. Keep in mind, this is a Digijet motor (pre 86), and not a dgifant (86 0n).

How does the auxillary air regulator function?

I know that it is a valve that is open during cold starts and closed once the motor is warm, but how do they actually work? Do metals inside the AAR expand from the effects of the engines heat and then force the valve shut, and when they cool down the valve opens? Or does the valve open and close via a signal from the 2 wires attached to it?

[Captain Pike]

12v heats a bimetal strip inside the reg to close the valve in cold temps.
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59 Panel bus, 1966 Single cab. 73' 181. 73 Westy. 91' H6 Vanagon 3.3L.
.....................All Current.......................

[shorepig]

[Randy in Maine]

If they work the same on a wasser as they do with an air cooled that is incorrect.

Cold it should be open, warm it should be shut.

http://www.type2.com/bartnik/tech.htm

[Captain Pike]

cold open,hot shut
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LEARN TO SELF RESCUE
59 Panel bus, 1966 Single cab. 73' 181. 73 Westy. 91' H6 Vanagon 3.3L.
.....................All Current.......................

[shorepig]

Ok, if an engine is cold, doesn't it need to be choked, or made more rich, by having more fuel and less air? If the engine is cold, then shouldn't the auxillary air regulator be closed, therefore preventing air from entering? When the engine gets hot, shouldn't the auxillary air regulator be open, to add more air, and therefore lean out the mixture?

[tencentlife]

The AAR is a variable throttle bypass. It allows metered air from after the AFM to take a route around the throttle valve. It has the same effect as opening the idle air adjustment screw a lot, or tipping the throttle open a bit. It has no direct effect on mixture, no differently than doing either of those things would. The ECU enriches warmup mixture according to engine temp, this is equally true of L-jet and Digijet. The AAR's purpose is to raise idle speed during warmup, not to alter mixture.

The only way the AAR has an impact on mixture is if air is leaking in at the hoses to and from it. These leaks would compromise mixture control whether the AAR was open or closed, since those hoses connect to the main intake tract at points after the AFM. Any air leaking in would be unmetered and so it would lean the base mixture proportionally.

The AAR is a simple gate valve. The gate is attached to a bimetallic spring. This is a strip of two dissimilar metals with different rates of heat expansion, laminated together. As a bimetallic strip warms, it bends because one side of it expands faster than the other, gradually closing the gate valve. This is the same method used to close off choke mechanisms on carburetors.

The strip is warmed from two sources: the body of the AAR being in direct contact with the engine case, and a resistive heat element inside the AAR that is fed 12V whenever the ignition is on. If the engine is cold, the strip is contracted and the gate valve is open. If the engine case is already warm, the strip is expanded either all or partially so the valve is closed or nearly closed, and idle speed will be raised little or not at all on a warm restart.

The electric heater warms the strip directly once the engine is started, so idle speed begins to go down on a time basis after a cold start, regardless of the engine case's external temp, because the engine internals are warming enough to support normal mixture combustion before the external surfaces of the engine case heat up very much.

If the electric heater element is broken, or not being fed power, the valve will still operate from contact heat, but that takes more time to cause it to close from a cold start. In this case, a cold engine may start fine and have a stable idle, but since the valve takes longer to warm and close from only contact heat, the idle speed will run higher as the engine warms and finally come down and stabilise once the engine case gets warm enough to close the valve. At no time does any of this have an effect on mixture; the ECU is measuring engine temp, airflow, and rpm and making its mixture adjustments the way it normally would; the volume of air passing thru the AAR has already been accounted for by the AFM.

That test procedure from Bentley is correct, but only if you expect the AAR to work just as designed. As I said, it will still work even if the electric element is broken or not receiving power, but the valve will take longer to close from a cold start, so there will be a period of too-high idle until the engine case warms enough to close the valve via direct contact.
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[jkeller]

Thanks Tencent! Another great description to help us understand the mysteries of these engines.
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1985 Weekender, Auto Trans.

[markz2004]

I learned something today !

Thanks for the nice write-up, among many others.
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87 Westy, 250k GW 2.4 - 2.0 , 16" wheels

[RCB]

If you dont have the rubber elbow that directs the hose to the outlett on the air intake hose, the hose really gets crunched in the little space its located in.
Getting an elbow makes things run much smoother.
Install hose clamps on every joint and make sure you also have the metal insert for the small rubber elbow.
The metal insert is installed on the upside of the aux air valve.

[camerahunter]

Reviving this thread with a question.
If I wanted to test this outside the Van how hot and how cold does it need to be?
Also, I can't seem to find it in the Bentley, complicated book it is . . .

Thank you,

David
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1984 - Daily driver

[r39o]

"Somewhere" (in print or on line) there was an article that described just how you went about testing the AAR. If I recall, and I can be wrong, the test was done using your home freezer and your kitchen oven.

The same article explained how to make a stuck one work and also how to set the screw on the side, too.

It could well be documented somewhere in Europen Car or one of the before titles to that publication.

Or online. Now that same gizmo is used on LOTS of cars. Rabbits had them some Golfs and I have even seen them in Nissans. So I will bet a procedure can be found out in the Ether somewhere.

FYI: 9 out of 10 are not working.....only in cold climates do you really need it.
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[Randy in Maine]

Here is a pretty good rap...

http://www.itinerant-air-cooled.com/viewtopic.php?f=50&t=7834

I used my freezer and hair dryer, but I don't know the temps right off hand.

[camerahunter]

I suppose it would help to mention that this is in a 85 1.9 engine.
There are no vacuum leaks that I can find but the idle is suddenly right around 1700 rpm. It does not have the throttle position switches on the top.
I think AAR is dead and needs to be working right.
It will idle correctly cold for a little while IF it doesn't stall. Once warn it's racing all the time.

Thank you,

David
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1984 - Daily driver

[r39o]

[binger59]

Sorry for the hijack but I have an idle damn near 3K until I unplug this valve. and then it goes to 1K. Same result if I leave it plugged in and unplug the AFM! This is quite frustrating wish I would have bought a 1.9 doh! Did I just say that outloud? does anyone have any thoughts? The thought of having to buy a Digital Stabilizer unit behind the tail light is very daunting to me, but I lean more towards that every time. I'm still learning this 2.1 stuff. The valve will stay unplugged till spring, when I pull the motor to do the water jackets.
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Binger

1984 Westy
1986 7 Pass R.I.P. Donor van
2019 Jetta
2014 Passat
2019 Atlas
2006 Passat R.I.P.
1998 Jetta R.I.P.
1984 Vanagon R.I.P.

[camerahunter]

I didn't think the 2.1 had this part.
Your problem could be as simple as your throttle position switch.
That or have you just tried to set the idle?

If I unplug the air line from mine on the 1.9 it kills the engine.
If I unplug the AFM it will still run but very rough.

The 2.1 is a different animal.
Does your AFM have a short cord between vans plug to the AFM?
Sometimes that will fix a poor idle.
However, 9 times out of ten it's either the TPS or just setting the idle correctly.

Thank you,

David
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1984 - Daily driver

[binger59]

No AFM filter on this air box and I took the throttle body of yesterday and gave it a good cleaning and the switch "clicks" just off idle and full throttle like it's supposed to. When you say set the idle what exactly are you referring to? I just stumped really.
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Binger

1984 Westy
1986 7 Pass R.I.P. Donor van
2019 Jetta
2014 Passat
2019 Atlas
2006 Passat R.I.P.
1998 Jetta R.I.P.
1984 Vanagon R.I.P.

[camerahunter]

Right across the center of the engine is the idle stabilizer, hose on the right, plugged in on the left. Unplug that while you run it and adjust the idle via the screw on the throttle body, to the right slower, to the left faster. Once set turn it off, plug it in and see if it's better.

Thank you,

David
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1984 - Daily driver

[binger59]

The screw in question would be the big slotted
Screw that adjusts the air by the butterfly in the the throttle correct? I'll try this tomorrow since it's dark here now. Thanks for the help.
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Binger

1984 Westy
1986 7 Pass R.I.P. Donor van
2019 Jetta
2014 Passat
2019 Atlas
2006 Passat R.I.P.
1998 Jetta R.I.P.
1984 Vanagon R.I.P.