I have tried blocking off this pipe. It will instantly give you ZERO power at low RPM and HAMMER the crap out of your MPG..... unless you get the chip tuned at the same time. $$$$$$$$$
This problem develops like clockwork at about 50,000 miles, and VW will do nothing for you. In fact, they had a RECALL of 2001-2005.5 Jettas for this EXACT PROBLEM, but refuse to issue a recall now.
As for federal emissions..... VW has a federally mandated emissions warranty of 20k and 80k. All parts are covered for 20k, but only a handful of specific components are covered for 80k. So even though the EGR cooler is only on the car to control NOx emissions, VW flat out refuses to do anything but spit at the customer when this problem occurs after the VW 50k or 4 yr warranty expires. The parts covered to 80k are:
http://www.epa.gov/oms/consumer/warr95fs.txt
There are three specified major emission control components,
covered for the first 8 years or 80,000 miles of vehicle use on 1995
and newer vehicles:
* Catalytic converters.
* The electronic emissions control unit or computer (ECU).
* The onboard emissions diagnostic device or computer (OBD).
In any case, has anyone explored the possibility of REMOVING this valve, but leaving the pipe in? I disconnected the vacuum actuator from the valve long (100k mi) ago and wired open the valve. The result was..... no engine problems whatsoever. Numerous inquiries to VW (good luck..) asking about the purpose of this valve have not yielded a result.
It appears that the valve simply restricts EGR flow at idle. The microsecond the gas is hit, this valve throws open. I don't see any benefit.
I didn't have the time to do a final fix, which is removing the valve flapper and sealing the hole, but I do now, and so I'm reviewing the forum. (I've driven for 110,000 miles with that damn hiss....) Just sealing off the hole sounds like a much more simple fix than having a bushing made, etc., and it's
free.