Handy930

What is the function of the AAV? I don't understand how the AAV works in conjunction with the AAR. My 930 is a California system. Any and all input greatly appreciated.

Mark Houghton

It's amazing how often this topic comes up. Here's a shot at your question: The air valve is just that...it lets meetered air into the intake plenum, just after the butterfly. Thus, leaning out the mixture to cause high idle. The air source comes from a hose connected to the intercooler and the air valve itself has a disc inside (remove the hose and you can see it)...that disc rotates to expose more or less of a "gap" to allow more or less air to pass through. The valve also has a heating element which heats a bi-metal spring, causing the valve (disc) to eventually close when warmed up.

Common problems are way too high...an idle that never goes back down even after the engine is warmed up. Usually indicative of a bad AAV, stuck open and not closing as it should. Or, the reverse...no high idle at cold startup, with a stuck closed valve. If yours is giving you trouble, you can remove the hose coming from the intercooler and look inside the AAV to see the position of the disc. There should be a gap/notch open when stone cold. Next, apply 12V DC to the connection and see if the disc with the notch opening closes off to almost completely (the shape of the notch is such that it will always be open just a little bit, even fully warmed up). It it doesn't close off, then the heating element is shot. Alternately, you can remove the AAV from the car and stick it an oven at a couple hundred degrees and observe the action of the disc.

Also typical of these amazing simple yet expensive devices is the tendency for the engine to idle high for a minute or so after restarting from fully warmed up. Apparently the residuel engine heat isn't enough to keep the valve completely closed, so upon re-starting the engine idles high for a period until the heating element does it's thing again.

Hope that helps!

Handy930

The valve you described I would call the AAR (auxiliary air regulator). What I am calling the AAV on my 930 is a diaphram valve that connects from the IC to the air intake past the butterfly. It has a vacuum connection through a thermal time switch that is open cold and closed warm. The USA model has the AAV connected the same way, but is not controlled through a thermal time switch. I have tested the AAR just as you discribed and it works OK. If I block off the air flow to the AAV it never seems to make any difference in the idle speed so I assume it is not working correctly. So I am lost as to what purpose it serves.

PorschePhD

The AAV aids in the start up. When it works correctly it opens on the initial load of the motor starting. This allows the extra fuel and air to surge to help the motor start and idle. When the car starts it will actually close off and shut. It it there just to aid and in most cases can be removed but may create a harder start or a bumpy start up

Handy930

Thanks for the the explanation. Its makes sense now that I don't see any difference with it blocked or not.

Mark Houghton

OOPS! Sorry, guess I wasn't paying attention. So with Stephens' description of the AAR function, what else could we ever need to know! To be honest, I always get the two mixed up...I often hear the AAR called an AAV, and vice-versa.

RarlyL8

Easy way to remeber - one is a regulator (AAR) and one is a valve (AAV).
Both allow for extra air around the throttle, one regulates flow (regulator) and one is an on/off switch (valve).

JFairman

It gets confusing to know which throttle bypass valve people are talking about online because the names of them get mixed up so much.
Maybe we should say the gold cad but usually corroded by rain and looks sort of grey after 20 years round steel one with the vacuum line on it, or the heavier odd shaped cast aluminum one with a wire plug going to it..

Looks like you asked what the round steel one with a vacuum line does.
That one is opened under high intake manifold vacuum when decelerating with your foot all the way off the gas by the small vacuum line. It then lets air bypass the throttle body making the engine not slow down as fast and also lowering emissions when decelerating.
Thats all it does and you can do the same effect by not taking your foot all the way off the gas when decelerating. Not easy to be consistant but that could be learned with practice if you wanted to do that.

The aluminum one with a wire going to it lets metered air from the intercooler bypass the throttle body into the intake manifold when the engine is cold. Being metered air that has gone through the airflow meter already it does not lean out the air fuel ratio to make a higher idle. It just lets more air into the engine bypassing the throttle body... again the effect is exactly the same as if you were holding the gas peddle down a little bit.
The mechanical and electrical operating action of it has already been explained in an earlier post above.

Lots of folks don't know that on later year cars with vacuum retard and vacuum/centrifical advance ignition distributors, the blue vacuum retard line is also disabled or blocked from going to the distributor's retard pot during and shortly after a cold or partially warm start by a small vacuum solenoid that is inline with it for around a minute (I've never timed it) by the k-jetronic box on the floor under the driver seat.
Then when that little vacuum solenoid is opened, intake manifold vacumm from below the closed throttle butterfly is allowed to go to the vacuum retard pot on the distributor, then the ignition timing retards a bit and the engine abruptly slows down about 400rpms.

Hope that helps.

Mark Houghton

[QUOTE=JFairman;6149521]Maybe we should say the gold cad but usually corroded by rain and looks sort of grey after 20 years round steel one with the vacuum line on it, or the heavier odd shaped cast aluminum one with a wire plug going to it.QUOTE]

Those descriptions work for me!
And thanks for the indepth description of just exactly how these things work. I'll be printing and saving a copy of this for future reference.