Need help with a vacuum diaphragm part

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Jan 15, 2009 | 04:03 PM

spoon2000

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AudiWorld Member

Joined: Dec 2003

Posts: 550

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From: Metro DC

Need help with a vacuum diaphragm part

<center><img src="http://pictureposter.audiworld.com/66527/p1000544.jpg"></center><p>On my 2000 4.2, there are a pair of small vacuum diaphragms at the front of the engine. They're connected by short black plastic rods to spring-loaded arms that pivot 90 degrees. I presume these have something to do with controling engine airflow at various operating temps and conditions. See the attached picture at http://pictureposter.audiworld.com/66527/p1000544.jpg

The lower/driver's side diaphragm has been stuck in the sucked-in position for over a year. I was able to push the spring-loaded arm back into position (i.e. make the diaphragm relax), but later the diaphragm would get stuck sucked in again. Around the time that the problem first existed, the car would rev very hard for a minute or two immediately after winter cold starts, then it would run OK.

This winter, however, the cold revving hasn't happened, and today when I looked at the engine, I realized that the black plastic connecting arm had broken. The spring loaded arm had relaxed (as if the diaphragm was relaxed).

What does this diaphragm do? Is there any harm in just leaving it dysfunctional and letting the pivoting arm stay relaxed full time (the other diaphragm seems to work fine)?

FWIW the car seems to spew a notable amount of smelly exhaust on start up...

Thanks.

Jan 15, 2009 | 04:56 PM

RLG

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Joined: Nov 2004

Posts: 4,212

Likes: 1

I think someone machined some alu arms a while back... STFA might help

I wouldn't know the best search terms to use, though.

If you end up needing any new parts to replace anything in that picture, let me know. I've got spares, used but perfect working order...

Jan 15, 2009 | 05:05 PM

tozoM8

AudiWorld Super User

Joined: Sep 2004

Posts: 6,716

Likes: 10

That's your variable intake runner. Here is your fix.

<ul><li><a href="https://forums.audiworld.com/a8/msgs/179821.phtml">https://forums.audiworld.com/a8/msgs/179821.phtml</a</li></ul>

Jan 15, 2009 | 11:50 PM

Stampy

AudiWorld Member

Joined: Feb 2008

Posts: 221

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From: Chicago

At 4K the arms switch over to the short length intake runner...

It is kind of a common issue for the 4.2. That being said, a lot of people don't even know they have one or both broken. So knowing that...its apparently doesn't really have an effect on anything other than your hp. If you STFA on here you will find a thread about a guy losing 30hp on an S6 because these were broken. They do serve a purpose, just a bad design by audi. I had the same problem, my passenger side was seized as well. I was able to work it loose and got some arms made by a guy here on AW. They are top notch, and won't break. Email me if you want his info.

<a href="http://photobucket.com" target="_blank"><img src="http://img.photobucket.com/albums/v431/stampy616/DSC00232.jpg" border="0" alt="Photobucket"></a>