Anti Shudder Valve - do I need it?

I've been trying to diagnosis a problem I've been having with my '02 Jetta TDI (http://forums.tdiclub.com/showthread.php?t=336357) that involves occasional heavy smoke/soot and low speed stumbling among other things. Since I've got 302,000 miles on the car i decided to replace the vacuum lines. Wow, I'm surprised the car ran as well as it did. I think it's likely there were multiple vacuum leaks.

My major discovery so far is that the ASV actuator doesn't appear to be working. The vacuum line was cracked and I thought that would be the end of it, but I decided to see if it would move with some vacuum. Surprise, surprise even with a new line and the Mitty Vac it will not hold a vacuum and doesn't open. Shouldn't I be able to get this to do something with the Mitty Vac. This may explain the clouds of soot that was ejected out the tail pipe the last time it ran in the garage. Maybe lots of vacuum would get it to open some but I can't hand pump the Mitty Vac that fast.

I realize it's job is to prevent run on but I can I live without it? I can only find it sold as part of the pricey EGR valve.

If the ASV does not work the only issue should be "dieseling" when you turn it off as it will run for a few seconds on whatever fuel it can find. The ASV does a momentary shutting of the ASV then releases it.

Clouds of soot are not related to ASV, EGR yes.

There are those who, like me, leave the ASV in as in the event of a turbo failure where the engine wants to run away, turning the key off kills the air to the system and the engine will stop. Without the ASV, off it goes.

Curious Chris said:

If the ASV does not work the only issue should be "dieseling" when you turn it off as it will run for a few seconds on whatever fuel it can find. The ASV does a momentary shutting of the ASV then releases it.

Clouds of soot are not related to ASV, EGR yes.

There are those who, like me, leave the ASV in as in the event of a turbo failure where the engine wants to run away, turning the key off kills the air to the system and the engine will stop. Without the ASV, off it goes.

Click to expand...

Ok, I would like to have a functioning ASV. Any idea where I can get a actuator without buying the entire EGR?

I think ID parts sells the actuators?

panda said:

My major discovery so far is that the ASV actuator doesn't appear to be working. The vacuum line was cracked and I thought that would be the end of it, but I decided to see if it would move with some vacuum. Surprise, surprise even with a new line and the Mitty Vac it will not hold a vacuum and doesn't open. Shouldn't I be able to get this to do something with the Mitty Vac. This may explain the clouds of soot that was ejected out the tail pipe the last time it ran in the garage. Maybe lots of vacuum would get it to open some but I can't hand pump the Mitty Vac that fast.

I realize it's job is to prevent run on but I can I live without it? I can only find it sold as part of the pricey EGR valve.

Click to expand...

I thought the ASV should be open with the engine at rest regardless of the key position. The ECU sends vacuum to it to hold it closed only as long as the engine is turning with the key off???

my 0.02
Agree with KLXD- The ASV is normally open, and gets pulled closed for a few seconds when the key is shut off. Also if I may, wish to clarify the first part of reply #2- When the key is shut off, the engine should immediately stop running and begin coasting down to a stop. The ASV pulling shut at that instant, helps the engine to coast smoothly to a stop without shaking the car (because during that time, the ASV is preventing the engine from sucking in air, which prevents the cylinders from compressing the air, which reduces shudder as the cylinders go through their compression strokes). With an ASV not closing on shutoff, the engine should still be observed to stop running immediately when the key is turned off. The difference will be that the car will be felt to shake, especially as the engine comes to a stop. The engine may be observed to move more, also (than when the ASV is properly working). Presence of the ASV is mainly for human "smoothness" factor, although the ASV can act as a safety shutoff device for a runaway diesel engine. Problem is in this instance, in case of a runaway, if the engine doesn't happen to fully stop within the few seconds offered by the ASV, the engine will pick up and run away again. But I guess that's sort of getting away from the symptom OP is trying to pursue... So, to OP- if you are finding your ASV shut when the car is off and / or vacuum hose is disconnected, that would be a problem. As a test, try (disconnecting the vacuum hose and...) wiring it / otherwise holding it open with something - wire or tape on the external lever etc. Drive the car, see if the issue goes away. An ASV valve flopping (partially) shut can indeed cause loss of power and black smoke.