Early ‘99 ALH Throttle Actuator Control Valve slow leak?

[TDI-Guy]

Early ‘99 ALH Mk4. Going into limp mode around 70 mph during sustained boost. I installed a new frequency valve I had, no change. Been testing for leaks and I vacuum tested the ‘throttle actuator control valve’ as it’s called out on my under hood vacuum schematic. Under vacuum it slowly leaks down. Not supposed to happen I’m guessing. Maybe it’s just me but I can’t seem to find this part listed for sale. Any suggestions? Can I safely bypass to see if it eliminates the car going into limp?

 

[TDI-Guy]

So some searching tells me this is an anti-shudder valve solenoid. Question still stands; can I safely bypass this thing and drive the car to see if it solves limp mode / vacuum leak? Also allowing me to maintain driving until the new part arrives? Any input would be greatly appreciated!

 

[ColbyM]

Your anti shutter valve is only used at shut down I'm pretty sure. Normally this shouldn't see vacuum until you turn the key off and it applies it to cut the air to engine for a smooth shutdown. Otherwise it's sprung open all the time.


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[BobnOH]

Is it this part?
I'd shop for a better price, but don't get a knock off.
If you disconnect and plug this, the vanes will stay wide open, no idea how it would drive like that.
If it's not that, but it is the anti-shudder valve, you can block/plug but you may need to to wire it open. Engine might diesel (run on) on shut down.
Perhaps someone who has actually done this will chime in.

 

[TDI-Guy]

Colby - thats correct I believe. The main feed is the port that leaks down while under vacuum, so if I’m interpreting it correctly, the system could still be seeing a vacuum leak even though the solenoid hasn’t actuated to close the valve. Which would make sense sorta seeing as it goes into limp mode while it’s under solid boost for a time.
BobnOH - no, I tested my VNT solenoid and it “seems” to be working correctly. Though I have not checked Hg on active and inactive positions.
Thanks to all for the quick replies!

 

[Nero Morg]

Have you checked your turbo actuator itself to see if it's leaking, doing a full range of motion, and moving and stopping at the correct vacuum values?

 

[TDI-Guy]

Nero - I have checked operation and holding vacuum, but not the pressure values at operation.
I did bypass the egr solenoid, no luck, car still goes into limp mode.
I have an extra VNT actuator, is there any special programming required to set it at the proper location? I don’t have VCDS currently, if that is required.

 

[BobnOH]

To adjust the actuator you need a vacuum pump and gauge. Adjust so it starts to move at 3.5 to 5 "/hg. To check the one you have on there, same thing, but first check it's not frozen and that it holds vacuum.

 

[Nero Morg]

Also, from my own experience, make sure the pivot bushing that the actuator arm has that attaches to the linkage isn't worn. Past that, do what BobnOH said. Your EGR bypass won't cause it to go into limp mode, unless you left the vacuum line uncapped.

 

[TDI-Guy]

Thanks guys. Gonna dig into it and see what I can find out. Gauge in my vac pump is broken, so I might have to figure smtg else out.

 

[ColbyM]

I don't know if you've seen this or maybe this is the diagram your using but I've found it helpful while troubleshooting vac system


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[Nero Morg]

Shoot forgot to also mention... Check the check valve (black and white pancake disc labeled #7 above) that it's working. And make sure you have sufficient vacuum. I've read some people say 22inhg is enough. I prefer 25.

 

[wonneber]

I have an extra VNT actuator, is there any special programming required to set it at the proper location? I don’t have VCDS currently, if that is required.

Follow the instructions given by BobnOH, you should be OK.

Check you have at least 20 inches of vacuum at point 5 in the diagram above.
Less then that it won't pull the arm all the way when needed.

The vacuum port on the vacuum pump (point 11 on the picture) will probably be loose. Some use silicon or epoxy to fix it.

Check the turbo actuator for rust and that it holds vacuum while you have it off.
There's a VW bulletin about this.

When you are re-installing it tie a piece of thread or dental floss to the e-clip that holds the actuator rod to the arm going into the turbo.
It makes it easier to find the clip if you slip putting it on.
I have a few in my body somewhere.

You really will need VCDS at some point to diagnose the car.
Limp mode alone can be from over boost or under boost.
If you have a laptop you could get VCDS lite.
The lite version if free to use and most functions work.
You would also need a OBD cable that works with VCDS.
some use the ELM328 (iIrc) with it.

 

[TDI-Guy]

Thanks to all for the help. I’m working through it slowly. After I replaced the VNT, it got better, but didn’t fix it completely. I have fixed the loose connection at the vacuum pump with silicone in the past, I should probably check it again. I have a few more vacuum lines to replace, need to order more vacuum line. I do have VCDS lite capability, tho my computer is down at the moment