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case proven i had same code pop up numerous times. popped the hood checked all lines and adjusted the screw to the left bout 1 turn (didnt know what way to turn it) car ran perfect.. hissing noise was gone and cel never popped up.. no cold start hesitation or anything.. im still gonna clean my passage and stuff but im happy now.. thank you
IF ANYONE REMEMBERS my post about the open vac line ........
that I had that bugged the hell outta me (not too far down page) I can use this to help explain myself better and maybe someone can help me. The line I have completely open is the connection at the EGRFV...the one that (in picture) has a black hose from it. I have the other end [of where that line would be] capped off at the TBody. This pics makes it appear that I can just as easily reconnect the line from point a to point b regardless of my intake lacking vac connections....kindda makes me feel stupid. But can someone explain whats happening with that line hanging open vs. if I simply reconnect it as it seems I should? why is my car running fine with that line wide open. thanks all.
further to what austinado16 said, its a source of atmosheric pressure that relieves the applied vacuum when the EGR F/V is "off" and allows the EGRV to close.
Some call this the Egr Mod and are happily running their cars this way. See the thread at link:
Some of these types of solenoids, have a simple plastic breathing cap on that rear fitting
Personally, I think having that fitting tied to the plenum is the huge contributor to the black gunk that glogs the EGR solenoid and it's hoses, restrictor valves, etc.
As you pointed out in your tests, you found a lot of black crap in the system blocking what limited vacuum is allowed through to begin with.
We've all seen the crud that builds up in the valve cover vent pipes, and then makes its way inside the plenum....and then into the intake manifold where it plugs everything up. Same thing is happening inside the EGR solenoid.
... yes, like the translucent one on the I/M C/O Valve. I want to see if both of those can be made to function here. Is the I/M C/O V just a different colour?
Re: the dirt, another reason to do the Cam Cover Breather Tubes mod.
Further, The "why" of the mod and the normal (as opposed to test) mode of the EGR system (as described in the reasons for the mod) are what I need to know more about. I thought the normal mode was strictly controlled by the duty cycle of the EGR F/V.
Last edited by Lago Blue; Dec 7, 2025 at 03:33 PM.
I am still a little confused. so ideally, the flow path comes FROM the plenum connection into the EGRFV and NOT from the EGRFV TO the plenum via the [black] vac line. Without realizing it I have then successfully completed the documented EGR modification, no?
If this is true, then what purpose is the EGRFV serving now and/or what function, if any, am I dissabling by having this mod?
To the 2nd (a very good question), I don't think I have the definative answer but here goes:
the EGR F/V functions (IMHO) exactly as before, but with a cleaner atmospheric pressure (vacuum relieving) air supply. Some may think that plenum vacuum is read and transmitted through this black line, and helps determine when the EGRV is tested but I am not so sure. Some EGR Systems use intake vacuum amplification to control the EGRV, I don't believe this is one of those. One reason for this is where that black line connects to the plenum on the B4, is there a spot between the MAF and T/B that could sense less vacuum? Probably not. A read through of the Mityvac manual speaks to some examples of the above.
Did Audi connect it this way because it is a possible un-metered air leak point into the engine if the EGR F/V should fail mechanically (the very type of seal failure austinado16 has illustrated) and it was open to atmosphere (like the I/M C/O valve is)? Perhaps.
Caution, wild-*** speculation follows:
Perhaps some have seen some relief by doing this mod because the EGR F/V if not yet failed, may tend to clean itself out inside when the supply of dirty relief air has been removed and replaced with a clean supply, allowing its' function to recover.
In my case, the EGR F/V internal seal has failed, it only works correctly intermittently, requires replacement because it does not seal reliably against vacuum, and leaks vacuum whether the ECU is asking the EGRV to open or not. This vacuum is also constantly leaking at the EGR F/V port which connects to that black hose.
Last edited by Lago Blue; Dec 14, 2025 at 06:48 AM.
Re: your 1st question....interesting, my man......
now does this mean, with the EGR mod done, that adjusting the VAC Reducing screw can/will still yeild results (whether good or bad), or is this screw now without a purpose.
...as before, fully in (clock-wise) should be most restricted, not entirely closing the passage IIRC (don't strip out the plastic housing threads!). Fully open ...(perhaps somewhere near screw-head top fully flush with raised plastic surround? Haven't figured that out yet.) ...still reduces the vacuum from that delivered from the intake manifold; and this adjusted amount will be reduced further (up-stream?) by the fixed black in-line ("x" orifice) restrictor at the EGR F/V end of the brown line.
Full I/M vacuum should not be nearly required nor would it be good for the long term health of your EGRV diaphram (see also the spec.'s in the manual). Despite the "x" restrictor, I could not reccomend by-passing this vacuum reducing valve, as I have not measured it's output alone. I don't yet have a reason to bypass the adjustable valve.
Found my adjusting screw O-ring being pulled off (up!) the screw -again- (and leaking vacuum, again!). There is a slight relief cut in the shank of the screw under the head and above the shank holes. Re-positioned the O-ring and re-installed the screw. Cleaned and -re-sealed the screw head in its raised plastic surround (with some goop) to prevent further leaks till my new EGR F/V arrives.
I am also wondering if this vacuum leak is causing slightly higher fuel pressures (and consequently; delivery) than we would want get; get otherwise? I believe full vacuum is required to get the FPR delivery down to 3.5 bar from 4.0. As the FPR shares the I/M vacuum source with this system, this is the reason for my suspicion, but I have not been able to measure that yet.
Lastly, I did read in an OBD II Training Manual that all the vacuum operated EGRV's are either positive or negative exhaust system back-pressure types, and that engine load will vary the diaphram control vacuum required (required vacuum in the brown line) to properly operate the EGRV. That is probably the reason for this adjusting screw, as these (EGRV's and EGR F/V's) are used on different engines (for instance the California Coupes have an EGR), they are probably set, and the screw -sealed-, at the factory for their specific application. Likely not something we should fiddle with.
Edit: Below is an updated illustration of what should more properly be called the EGR Frequency Valve Vent Mod:
Last edited by Lago Blue; Dec 14, 2025 at 06:59 AM.
Audi Recreates Crazy-Looking Speed Record Breaker From 1935
Slideshow: Audi has recreated one of the wildest machines of the pre-war speed-record era, reviving a streamlined V16 racer that originally exceeded 200 mph in 1935.
Re: code 2411 re-visited...
