Auxiliary air valve

[Blaise]

I am trying to track down a poor idle on my 1980 528i and am tackling one possible culprit at a time.

Today, it is the auxiliary air valve. As I understand it, it lets some air past the throttle plate at cold idle. When the engine warms up, the valve shuts and air no longer bypasses the throttle plate (unless one turns on the A/C....right?)

This auxiliary air valve heats up with the engine in two ways. It is bolted to the valve cover and heats up with it AND it has a heating element in it that is triggered when the ignition is turned on.

In my case, the threads in the valve cover were stripped. If you are interested, here was my repair.

http://picasaweb.google.com/blaisedesco ... directlink

I was interested in how the auxiliary air valve works, or if mine works properly. So, I put my map torch to it (gently) and did watch the valve close. It was a bit jerky, but it closed.

What I noticed is that it really does not open fully when cold. Here is a photo of it when cold:

<table><tr><td><a href="http://picasaweb.google.com/lh/photo/gy ... site"><img src="http://lh3.ggpht.com/_UZQuuBHQvx4/TNY3F ... C08026.JPG" height="300" width="400"></a></td></tr><tr><td>From <a href="http://picasaweb.google.com/blaisedesco ... -auxiliary air valve</a></td></tr></table>

When hot, one cannot see through it, but I can still blow air through it. Is this normal? I imagine that this does not matter, as this is past the AFM and is "metered" and in turn the injectors compensate.

<table><tr><td><a href="http://picasaweb.google.com/lh/photo/SG ... site"><img src="http://lh5.ggpht.com/_UZQuuBHQvx4/TNY3E ... C08019.JPG" height="300" width="400"></a></td></tr><tr><td>From <a href="http://picasaweb.google.com/blaisedesco ... -auxiliary air valve</a></td></tr></table>

I sprayed a little solvent in there and blew it out with my compressor. I found that this valved leaked at the entire perimeter of rounded disc. Is this normal? Since this feeds into the intake log, I imagine that this would essentially be a vacuum leak. Could this be the source of my poor idle?

[JoshInAtlanta]

Blaise,

I was fighting a similar issue earlier this year. I pulled the AAV off the car and cleaned it in a similar way, tested it, etc. Still didn't really help.

Mine did not leak around the perimeter, but it was like yours in that it did not fully open. I got a spare off a parts car, swapped it on, and problem solved.

I think I have two more spares in the garage. If you've still got idle issues, let me know and I can dig around. You're welcome to try one out and see if it makes a difference... certainly better than spending $100+ on a new part!

[T.Hanson]

Now I'm all confused. What does the exterior nut do, and if clean, working inside, adjust what which way to have what happen ?

My '81 with valve cover style aux air, was doing the idle zoom, kill, drop, search deal. Took it off, it looked like your photo. Not fully open (cold), not fully closed. Heat it up, I swear it opened but I could be wrong.

I thought the object was less air, richer mixture on start, valve closed. Squirted carb leaner, rust-o-laxo-lube, used air gun to clean out.

What tightening or loosening the exterior nut did, looser seemed to allow the valve to close more than it was (cold). Starts now sits @ 800 rpm, no zooming, searching. If I'm picky the 800 seems a dab low, lumpy, but it takes throttle without major stumbling, gets right pretty quickly.

Three AFM's, noodling with the Aux air, full throttle body adjust, new fuel pumps, fuel pressure regulator, O2, sensors checks, grounds, injector fuel lines, main lines, it's still not what I imagine factory new perfect was like.

Still a dab sensitive, low, minor lumpy, cold start idle, but for me it's, " Stop noodling and drive around the futseys.

[Blaise]

Now I'm all confused. What does the exterior nut do, and if clean, working inside, adjust what which way to have what happen ?

My '81 with valve cover style aux air, was doing the idle zoom, kill, drop, search deal. Took it off, it looked like your photo. Not fully open (cold), not fully closed. Heat it up, I swear it opened but I could be wrong.

I thought the object was less air, richer mixture on start, valve closed. Squirted carb leaner, rust-o-laxo-lube, used air gun to clean out.

What tightening or loosening the exterior nut did, looser seemed to allow the valve to close more than it was (cold). Starts now sits @ 800 rpm, no zooming, searching. If I'm picky the 800 seems a dab low, lumpy, but it takes throttle without major stumbling, gets right pretty quickly.

Three AFM's, noodling with the Aux air, full throttle body adjust, new fuel pumps, fuel pressure regulator, O2, sensors checks, grounds, injector fuel lines, main lines, it's still not what I imagine factory new perfect was like.

Still a dab sensitive, low, minor lumpy, cold start idle, but for me it's, " Stop noodling and drive around the futseys.

This should help clear things up:

http://www.firstfives.org/faq/aux_air_v ... valve.html

The valve should let air through when the car is cold....which is similar to you stepping on the gas pedal a bit (opening the throttle plate a bit).

That adjustment screw is not obvious at first. The tightening and loosening of the screw is not the adjustment....that just locks it in place. The whole shaft actually slides side to side....opening or closing the valve a little. Away from the main body of the valve opens the valve. I believe that this is a small adjustment to the amount of air that comes through at cold idle. Loosen the screw and move the shaft....and let us know if the idle speed changes.

Heating the valve progressively closes it.

Hope that helps

[DEMIURGE]

As I know - this air valve is called an "additional air valve" and it is powered with the seventh injector (cold start), driven from the same cold start relay.
This additional volume of the air is to compensate the very rich mixture in the plenum, caused by the cold start injector.

My additional air valve in cold conditions is simillary not fully open. Beside heating, you can apply 12V to check the "electrical" opening.

The causes for a poor idle could be not only a mixtures problems (including vacuum leaking). It could be engine and fuel problems.

[Mike W.]

At worst it should only affect idle speed as it's metered air, so mixture doesn't change.