Testing Auxiliary Air Valve (AAV)

pub911 · 03:35 PM

How do you test if an AAV is operational? I have a BOSCH 0280 160 400 that doesn't close when i attach a house vacuum cleaner to it. The CIS Primer says it should "pull a vacuum at 8" ". And I have read that the intent of this component is to provide a 'gulp of air' at start-up and then close.

I'm experiencing a high idle and rough running - misfiring - until i get up to about 3,000rmp. This appears to be consistent with a bad AAV. It's also consistent with a big vacuum leak which i've been unable to locate elsewhere.

Oh, and if I suck on it - yes, you read me right - it doesn't close either. FYI, i'm applying suction to larger of the two pipes, the one that is NOT in the center of the AAV.

Just so we're all on the same page, I'm referring to the flying-saucer shaped thing that sits behind the airbox towards the passenger side of the engine. I am not referring to the AAR which has a 12v plug attached to it. The AAV is a mechanical device only - no electrical connection.

tirwin · tirwin's Garage

CIS Troubleshooting for Dummies

See post #16 for link.

pub911 · 05-02-2016, 05:10 PM

got it! thank you.

pub911 · 05-02-2016, 06:17 PM

Follow-up question. The aav test says it should pull 5"-6" - is that inches of Hg or H2O? I can't see the gauge in the picture. thanks!

pub911 · 05-02-2016, 06:19 PM

I don't have a mity vac in hand, by the way. My household vacuum cleaner struggles to pull the valve closed, but it does eventually, then my vacuum gives up and the valve releases. This process repeats itself. Have I given you enough to tell me if my AAV is faulty?

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by pub911

Follow-up question. The aav test says it should pull 5"-6" - is that inches of Hg or H2O? I can't see the gauge in the picture. thanks!

" Hg.

Tony

T77911S · 05-03-2016, 03:44 AM

its been a while, and I did not know jim replied to that post too, but once the AAV is pulled in and closed, you should be able to remove your hand and it should hold closed.
I don't think the 5-6 really matters. you just want to make sure it closes and holds the vacuum.
been a while since I tested one.
the hand vac is a GREAT tool to have. I did not think I would use one that much but I do.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by T77911S

its been a while, and I did not know jim replied to that post too, but once the AAV is pulled in and closed, you should be able to remove your hand and it should hold closed.
I don't think the 5-6 really matters. you just want to make sure it closes and holds the vacuum.
been a while since I tested one.
the hand vac is a GREAT tool to have. I did not think I would use one that much but I do.

Ty,

The low vacuum is needed to close the AAV as soon as the engine starts to run. If the AAR requires a much higher vacuum to close, it would not immediately shut off after start. This is the main reason the AAV is set at this low vacuum pressure. Typically, between 6 - 8" Hg is the operating pressure I observed in my previous tests too. Feel free to contradict this observation.

Tony

T77911S · 05-03-2016, 07:02 AM

that's ok
I did not think they were adjustable so the real concern is that they don't leak. if they don't leak and they close, I would think they work as they should. I certainly would not trash one that did not leak but took a little more than 6-8" as long as it closed and stayed closed.
I know I am more flexible on things like the 6-8, but also I have not tested as many as you have.