vtraudt

Always wondered what this valve is that sits on top of the throttle body, has vac lines connected and a white plastic adjustment ****.

What is that part doing?
How is it called?
What is the adjustment know for?
How to properly set it?

grillage

EGR solenoid

026906283H

Like this one?

http://www.ebay.com/itm/VW-Audi-EGR-...-/130519461099

vtraudt

Nope. Mine has (I will check again and take a better picture) an adjustment know (and IIRC only 2 vac connections).

grillage

I found one in my basement. The "adjustment" is actually a cap over another valve...



I cleaned the one side up to confirm part number...

Lago Blue

It is the Intake manifold change-over (solenoid) valve (aka: N154)

Pretty self-explanatory. It uses vacuum stored in the infamous leaky vac. reservoir to open the six butterflies.

see drawing here:

("This coloured diag. connects the dots for you...")
https://www.audiworld.com/forums/sho...51&postcount=7

Grillage is right in that the white item is a cap, it does turn but is not an adjustment ****. However it is a -vented- cap; and you should perhaps employ another one on your EGR Freq. Valve to function likewise after you do the Freq. Valve Vent Line removal mod (formerly the EGR Mod).

Further reading here:

("Code 2411 re-visited...")
https://www.audiworld.com/forums/sho...php?p=22438033

upallnight

It's an EGR solenoid valve that controls vacuum to the EGR valve. The "adjustment cap" is not an adjustment cap, but just a cap over another port so that there will be no vacuum leak since that port isn't being used by the EGR system. This valve is found in other system, hence the cap over the port that is not being used.

Someone replaced the cloth cover vacuum hoses with what appears to be blue silicone hoses.

vtraudt

I took the cloth vac lines off (brittle) and replace with silicone.

Could this valve be responsible for the still unresolved issue of getting only 10-14 mpg?

Spark plugs did not indicate 'filthy rich'.
No codes.
Downstream O2 sensors replace (had code).
But find 'milky' slime in the valve cover plastic corrugated vent hose.
Plus quite a bit of white (steam) smoke. In winter not just during cold start, but even when warm.

Lago Blue

Good guess sir but I'm afraid it is not. The EGR Frequency Valve (aka: N18) is -also- clearly visible in the bottom RH corner of the first two photos, recognizable by the unique extra black plastic "X" housing attached to said valve as per the drawing I attached earlier.

Further, that cap cannot prevent a vacuum leak as it is purposefully a vented cap designed to allow airflow. Once removed one can see 3 vent slots around and connected to the central bore. In use this cap allows vacuum relief via the necessary port it guards from "FOD" for the manifold change-over function. When the engine requires the long intake path, the vacuum used to hold it to short path is relieved here.

Lago Blue

By itself, probably not. However it may leak vacuum, so it may contribute some loss. You must prove its serviceability. A leak-down test will tell you. However here is not where I would look first.

Consider that the cause of your poor mileage may be several things combined.

I would start here:

a.) What does your engine pull for vacuum in inches of whatever when fully warm?

b.) Do a tour, survey and fix as follows. In the thread below, go to post #34 first, then read the rest of them only as required;

https://www.audiworld.com/forums/sho...ht=tour+intake

c.) Report back your results.

Hope this helps.