jroczniak

Found this broken part today. The linkage rod is no longer attached to the valve-cover type part it should be attached to.

I need to replace this but no one I know has any clue at all what I need to do or what this is!

Thanks in advance for the help!

Jake R.

spoon2000

Jake,

Voila. What you've photographed could well be the source of your cold start problem. The part at the right in your pic is a bellows (or "motor" in some people's lingo) that gets sucked in by vacuum pressure and in doing so pulls the black plastic "dog bone" linkage. That linkage piece in turn causes one of the sets of vanes to rotate about 90 degrees and close inside your header and change the amount of air getting sucked into the combustion chambers. In your case, the linkage is obviously broken off where it attaches to the rubber bellows. As a result, your vanes are in the wrong position as the car first starts, leading to an incorrect fuel air mixture when the engine is trying to calibrate itself. The result is the cold start surging you and I have both experienced.

The bellows for the other side of the engine is at the lower left corner of your photo. Examine the positions of the bellows with the engine running and not running and you should see a difference (I think the bellows get sucked in when the car is on, and then they're supposed to release when you hit 5000 RPM or so).

Can you manipulate the dog bone back and forth by hand from left to right (as you're facing the car)? It's not necessarily easy, as the shaft is spring loaded and is under some pressure. If so, figure out a way to pull on the dog bone such that it gets into the position it would be in if the bellows was sucked in and wire it in that position somehow. Then just drive the car like that and see what effect it has on your cold start problem. If you can't move the mechanism easily by hand (which is probably the case, otherwise the dog bone piece wouldn't have broken off from the bellows), you'll have to do some additional disassembly of the shaft controlling the vanes and work it back and forth by hand and with WD-40 until it moves more easily (see my other posts on the subject for more detail on this).

I would not worry about getting the bellows replaced as IIRC it's a stupidly expensive part, and, assuming your vanes are in the right position (which they're presently not) its proper function only relevant on those rare occasions when you really floor the gas pedal and get over 5000 RPM.

None of this is complicated, you just have to work through it, so don't be intimidated and don't be afraid to ask for more help in the forum.

spoon2000

See my pic in post 12 of thread https://www.audiworld.com/forums/sho....php?t=2783439 for what things are supposed to look like. There's other good info in there, too, in other people's comments.

jroczniak

When you say to "wire it in that position somehow", if I can re-attach the end of the dog bone back to the top of the bellow, is that ok? I think I can do it with some wire perhaps.

spoon2000

That is OK IF you've made certain that the changeover valve vanes are turning back and forth freely. Otherwise, something else is going to give (like the dogbone or the rubber on the bellows) and you'll be right back where you started from. What I was really thinking of when I suggested wiring it in place was to fix it permanently in the normal sub-5000 RPM running position.

jroczniak

Well it seems to already be stuck in the position you said to move it into... I couldn't move it back the other way. The other one moves.

spoon2000

Hmmm. Interesting.

Does the one that moves go from one extreme to the other when the car is off vs. on?

Do both bellows inflate and deflate when the car is off vs. on?

What happens when you pull the vacuum hoses off after you've shut off the engine -- do the bellows move (i.e. release and inflate) again?

When you say you couldn't move the stuck changeover valve back the other way -- did you remove any other hardware (bellows, linkage rods, vacuum hoses, etc.) and try to move the black plastic triangular-shaped arm with a tool like channel lock pliers, or were you just reaching around the existing hardware to try and manipulate it with your fingers? I ask because, depending on how long the thing's been stuck in one position, it may be a bit difficult to get loose at first. And then getting it loosened up again may take several hundred swings of it back and forth (mine did, and I wasn't sure I was making any progress at first, but it got easier over time). Considering that you're still having cold start problems, I think it would be worth it to try to loosen up that changeover valve to see if you can make a difference in how the engine behaves. The best of all outcomes would be for you to get that valve loosened up and then to connect it to the vacuum bellows with some rigged-up solution like I did on mine so that it works pretty much as the Audi engineers designed it to.

Hang in there and have faith!

spoon2000

BTW, if/when you get to the point of removing the center bolt on the changeover valve (the silver one that takes a Torx driver) and slide the valve shaft/rod toward the front of the car to help loosen things up, don't freak out if the road won't immediately go back in easily. It takes some trial and error to seat the other end of the rod (the one closest to the windshield) in the notch that it sits in on the rear-most wall of the engine, but you'll get it eventually.

SloopJohnB@mac.com

I don't think so. I've had Three (count-em..3) such failures and NONE of them affected the cold or hot start and indeed were hardly noticeable until a CEL came on long after the failure. Those vanes only alter the length of the intake runner tract to the intake ports.

Unless the vacuum motor diaphragm is ruptured, it shouldn't even throw a CEL!!

The cure is spendy-to-expensive...a kit that replaces the two diaphragm motors and the dogbones..~$750 plus labor, or a new manifold (comes with etc.) installed about $1600.

There is a possibly less expensive fix...the arms that the dogbones actuate is held onto the rod that has the internal vanes by a torx or allen-head bolt...in your pic it's about an inch to the left and down from the end of the dogbone. In real life it's about two inches.

Some people have had good luck removing the dogbones, unscrewing the arm bolts and removing the arms and cleaning out/around the aluminum arms the corrosion that builds up underneath them. In other words, the arm is causing the failure to move rather than a frozen rod. You'll still have to find dogbones if one broke or diaphragm motors (good luck on new ones..new motors only come with the $700 kit) but you might be able to get used motors from shokan.com or buy an entire used manifold. A used manifold goes for about $300 or so on ebay.

jroczniak

I will try to disassemble everything this weekend. I think my biggest challenge is going to be that the dog-bone did not break, the metal piece that connects it to the diaphram did so I am not sure how I could reconnect it once I loosen it all up.