I was getting intermittent Check Engine Light 16785 EGR system insufficient flow.This would occur 15 to 20 minutes into a trip when car was warmed up. Usually would trip the light as I accelerated between 2000 - 4000 RPM.Problem would occur more often when it was raining or cold outside. Dealer told me it was probably EGR valve ($220 + labor). It wasn't. Fixed for less than $20. EGR valve is very simple item used on a lot of older VW and Audi motors. Part very rarely fails. If you have more than 70 Kmiles the EGR passage in the manifold gets blocked up with carbon deposits.

EGR and throttle body gasket from dealer $8, Can of Gumout throttle body cleaner $4. 10 feet of braided vac hose $8.I didn't count the tool prices.Only weird tool you need is a 22mm claw foot wrench to remove the EGR valve(make sure it's an open claw not a flared type). Sears sells a 7/8 (close enough) crow foot for about $7.You take off the throttle body first (4 6mm allen bolts) and then after loosening the heat shield (I have an A4 so it might be a little different)you should have enough room to get the crow foot wrench in there.A universal joint on your socket comes in useful here.Then there are two 10mm hex bolts that hold the EGR on to the manifold. Once you have TB and EGR off there is a passage that goes horizontally under the manifold then makes a right turn up into the inlet manifold just in front of the TB. A lot of crap gets stuck at the point where the EGR gases (and the oil condensates from the plenum) hit the manifold. Using a piece of wire and gumout and using a 1/4 drill bit turned by hand you can clean it out.Clean out the EGR valve too. Vacuum it all out afterwards.Clean everything up ,fit the new gaskets and vacuum line and you are done.Takes a couple of hours.Obviously there is some other junk to remove to get to the TB and EGR but I don't know how your car is laid out under the hood.

after follwoing Mike's excellent instructions for getting to the bore that needs unplugged, buy 18" of some 1/8"-3/16" braided cable. You know, the kind used on wenches (only smaller) and bicycle locks etc. Unravel the strands at one end and flare them out slightly. Then chuck the other end up in an electric drill. Get the end that has the flared strands into the hole by holding all the strands together with your fingers. Once inside start the electric drill slowly and feed the cable into the port. It completely scrubs the interanl passage clean. Roto-Rooter clean. I mean "clean" as in brand new car clean. It's the best trick in the world for cleaning the EGR passage. No other chemicals required or needed. You will not believe the crap inside that thing! Oh and only power the drill up when feeding the line... not when pulling it back out. It makes a HUGE mess with centrifugal slinging. Voice of experience here.

Someone suggested that in earlier post but I did not trust myself with a power drill in case I overdid it.
About how often have you cleaned it? People have told me about 70K miles or so, although I imagine as the motor gets older there is probably more crankcase vent oil getting in.

The EGR valve was clogged with carbon deposits.
Had I known back then about the below-mentioned procedure, I would have done that and replaced or cleaned the EGR valve myself.

I almost bought a used one for $75 until I realised when I looked at the valve at the junkyard counter it would be hard for this to be broke.

The car did idle a bit better with the new EGR valve, but not for long. In the end, I ended up cleaning the ICV and MAF, and that seemed to make a much bigger difference. I really can't tell in how far the EGR valve was the culprit...

iam getting ready to do a bunch of Maintenance as well as a custom intake and heatsheild, just waiting on the maf adapter to be made. so all this info helps very much.

anyone have a picture of the stock plastic plenum tubing that goes to the throttle body showing the vacuum hoses? I'll tell you what to pull out ;)

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Ok, see that yellow vacuum solenoid switch sitting loosely above the intake change over diaphragm which is on top of the cruise control motor?

Hmmm, let's start again. That yellow vacuum control diagram is the EGR control solenoid. As you can see it has 5 connections.

Connection #1 is the hose that goes over the intake switchover valve and then disappears below as it connects to the EGR diaphragm. This is how you test if the EGR is working. You disconnect this hose and with a mighty vacuum pump, let the engine idle, apply vacuum in there and see if the car dies or idles very rough. If no response, your EGR ports are clogged up or if the mighty vac cannot apply vacuum - then the diaphragm is ripped.
Again, like I said, your EGR needs to be working so that no CEL will happen.

Ok let's move over to connection #2. It has a U shape hose that goes to connection #3. That was easy :) Anyway, that port of connection #2 is the switched port by the solenoid. This is how the ECU will determine "test mode" or "normal mod" - I mean mode :)

Connection #4 - is behind the yellow solenoid and it seems to disappears underneath that light blue and black one way valve (there's too much blue and black in this pic hehe). That hoes 'T's with the vacuum reservoir located in front of the engine next to the coil pack (1.8T's don't have 'coil packs' - just 'coils', we do ;). Why does a EGR need a constant vacuum source? It doesn't during normal mod. It's only for testing - aha!

So what is connection #5? eh ah dum dee doo - [unplug, seal] :^ That goes to - on a stock tubing, post throttle body port. The stock tubing leading to the MAF senses vacuum when you accelerate. This is amplified by that solenoid switch (it's not just a vacuum switch) using the stored vacuum. This in turn will create enough vacuum during acceleration to open the EGR valve.

Why does the light not go on? Because the trick is when Motronic will 'test' the EGR. During idle or random cruising speeds, it will cycle the solenoid and connect stored vacuum to the EGR. It will measure a drop in rpm and increased EGR temps (via the sensor) and if there is change, the ECU is happy. Then it will switch back to normal mod. Removing the port to the intake track will eliminate the EGR from opening during acceleration, so instead of getting a mix of 10% warm inert exhaust gas in the intake stream, you fill it in with 100% 14.7 :1 of pure air/fuel mixture.

Hope that helps - free power is king :P

of recirculated EG at WOT again? Wasnt it like 15-20% last time I looked into it?

I totally forgot..