OK, in a nutshell, here is a quick rundown of how the ALH's EGR works:
It uses vacuum to operate the EGR valve itself, the vacuum source is from the mechanical vacuum pump at the end of the head, the same one that supplies vacuum to operate the brake boost, the turbocharger control, and the anti-shudder valve.
The vacuum is controlled via duty cycle of a solenoid on the firewall. Full ON and all the source vacuum available goes to the EGR valve, pulling it open. Full OFF and all the source vacuum is stopped, and vented to the vent side of the system which is shared with the turbo solenoid (which works the same way). This vent side goes to the 'clean' side of the air filter, right under the MAF connection.
The engine is just an air pump. When the ECU turns on the EGR, more air will be coming into the engine via the pressurized exhaust side than there would be with it off, and the ECU detects this via watching the MAF value. EGR off, MAF value is higher.
Now for some reason, Bosch and/or VAG got confused as to the fault criteria nomenclature for EGR, and all too often an "excessive EGR flow" really means "excessive MAF flow", and in actuality the EGR is not flowing enough, or at all.
Now if you have neutered the EGR system, we already know the ECU is seeing not enough EGR flow. So in order to find your problem, you need to put it back to how it left the factory. There is a vacuum diagram on a sticker under the hood, near the hood latch, although I realize that by now many of these are not legible. Luckily, if you search you can easily find this on the internet. Google image search "ALH vacuum diagram" and you will find it if you do not have a manual that has it. The ALH is brutally simple, and the EGR system is as simple as they come really.
Once you have verified all the vacuum line connections are correct, check the EGR valve operation. You can do this a couple ways. To verify the valve itself actually works, connect a vacuum pump directly do it, and pump it up. It should both open and hold vacuum (take the charge air hose off and look inside to see it opening...with the engine off, obviously). If that checks good, then move on to the control side.
Put it back together, start the engine up and run it for a couple minutes (depending on how cold it is, you may want to drive it for a bit).
Then, with it idling, but within a minute or so of it being higher than idle, pull the vacuum line to the EGR off...it should have vacuum, and the EGR valve should have been open, so when you pull that line off, you'll hear a change in pitch of the engine when the valve closes.
If you don't, then you need to see where your vacuum loss is. Could simply be a bad control solenoid. You can temporarily swap it with the one for the turbo and retest. We know the wiring to it is OK, or the ECU would have a different fault.
A scan tool will also show EGR data, via actual and requested MAF values (VCDS has it labeled). Remember, EGR shuts off normally after a couple minutes of idle time.
