Bill's EFI Drama AKA A Game of Name that Component!

[Captain Obvious]

Something to think about is that by pulling the hose off the AAR and letting air in, what you are doing is leaning out your mixture more than anything else. So if it sputters and struggles at 400 RPM when cold, but it runs great if you let in some unmetered air (air that did not go through the AFM), I would be looking for a mixture problem, not an AAR problem.

It sounds like you're running way rich at idle and drowning the motor. By opening the hose and that letting air in, you're raising your A/F mixture, and apparently your engine likes that.

[Captain Obvious]

Something else quick. You probably know this already, but just to make sure there's no misunderstanding...

All the AAR does is allow air to bypass around the butterfly plate in the throttle body. With the exception that the AAR doesn't affect the TPS switch, it's exactly the same thing as sitting there with your foot on the gas pedal. It has no effect on mixture.

So the only difference between opening the throttle plate by pushing the gas pedal down a little and having an opening through the AAR is that if you push the gas pedal down far enough, you will open the TPS idle switch (which would raise the A/F ratio a little). Other than that... No difference.

It's just convenient because you don't have to sit there with your foot on the gas as the engine warms up.

[mentalite]

I'm with you, Captain.  Unfortunately your theory turns what I thought to be a fairly simple problem into a complex one.

[Zed Head]

On 2/23/2017 at 7:12 PM, mentalite said:

Less than 0 degrees F in the freezer:

And this is the extent of the opening:

I'm expecting this to be fully open at this temperature.  Is my expectation valid?

Does it close?  That's the important part because it's the only thing that makes it different from the idle speed air bypass screw, which also does what CO described for the AAR.  You should be able to raise your idle speed by turning the idle speed screw.  But it will stay high after the engine warms up.  The AAR doesn't stay open very long, it has its own internal heater that closes it well before the engine gets to operating temperature.  If you connect a battery to the terminals you can watch it close if it's working correctly.  Some people remove them and just hold the throttle open for a short while.  As Captain impled, it has very little affect on how the engine runs.  It's just a convenience.

[mentalite]

The new one closes all the way, the old one didn't.  The car idles and runs good after it warms up.

[Zed Head]

3 hours ago, mentalite said:

The car idles and runs good after it warms up.

Not really clear what the problem is then.  Sounds like you're saying that the idle just isn't high enough to keep the engine running when it's cold.  Is that it?

Another possibility is that the AAR hose is connected wrongly or it's clogged.  It really is a very simple system.  You could replace it with a cable-actuated valve and a hand lever if you wanted.  That's how simple the concept is.  The engineering that makes it automatic is the bimetal strip inside that opens and closes it based on temperature.

But.  Could be that you actually have a PCV system leak that's overpowering the AAR effect.  Your engine might have been tuned around a broken PCV system.  Maybe you should do some PCV system checks.