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It should have a steady 12v when tested from the red/blue wire to ground but if tested on both terminals with a test light you should get a rapid pulse when the n-80 is active. The ground goes to #31 on t68 from the ecu (J220). With engine off the n-80 is closed. The purge valve has an arrow that indicates the direction of flow and it has a small internal filter on the intake side.The evap cannister has 3 hose connections and is found to the rear in the left front wheel well. 
Two connections clip, and the third is a rubber friction fit that goes out the back of the cannister. The rollover valve will close if fuel enters the vent through the top of the filler neck. If you over fill your fuel tank fuel can enter the evap system through this clear vent line causing gurgling, filling problems, and or evap codes. If you look to the left wheel well from the rear you can see a loop in the clear tubing where the fuel overflow can be drained. 
There is a flow check and on the tank two vents, one near the filler and one near the fuel pump. Off the back of the evap cannister the line tees and goes to the leak detection pump (ldp) and the n-115 vent valve. 
The n-115 is open when the engine is off. The 12v power is the pin 1 red/blue and the ground is pin 2 switched with a relay (j490) in the center of the dash. The ground is shared with the leak detection pump and it is controlled by the ecu on pin #35 on the t68 so the relay is energized and the n-115 vent valve is closed when the ldp vaccum solenoid is powered. To access the n-115 you need to drop the fuel tank. To drop the tank simply remove the rubber grommet from arround the filler neck, remove the bolt securing the neck, support the tank, then remove the four 13mm bolts on the tank straps. The pins should have in the range of 25 to 40 ohms resistance I am not sure what the offical numbers are but that is what I expect to see (same with the pin2 pin3 on the ldp and pin1 pin2 on the n80). The ldp is a pump driven with vacuum from the hard 1/4in black vaccum line in the front left engine compartment that tees in to the brake booster vaccum line.
The solenoid is energized in pin 3 and the circuit is completed via pin 2 when the ecu opens the path to ground. Pin 1 on the ldp is a pressure switch. It sends a ground signal to the ecu on the #46 pin of the t68 when the system reaches pressure and opens if there is a leak. The lower pipe on the ldp tees to the vent tubing on the inner frame rail. The ldp test can be activated with the vagcom (01 engine group 71 basic settings). When the ldp is activated the n80 and n115 will be closed. The ldp will tick for a minute or two depending on the fuel level in the tank.
If it continues to run or it stops then restarts there is a leak in the system and a leak code will be set as a pending code. After a minute or so if the system maintains pressure the n115 will vent and the n80 purge will eventually open and the vaccum will pull the fule vapor out of the cannister and burn it in the engine. If you get a leak code first try the obvious; clear the codes, check the gas cap, and n80 for leaks then run the evap test with the vag. Behind the left headlight in the battery compartment you can find the four pin T4e/ terminal that connects the wires from the ldp and n115 to the harness that goes through the firewall.
I will edit this post to add more details and pics when I get some more time.
If you do not find a leak check air filter then your maf and b1s1 o2 sensor output since the feedback from those sensors primarily determine adjustments to the fuel air ratios. The adjustmens in the short term fuel regulation do not usally effect cold start. Beyond that could be clogged injectors, or fuel filter. The fuel rail pressure test will tell you if adequate fuel is being delivered to the injectors.
(I washed my van when it was below zero and water got on the alternator froze it up and popped the belt.) I dropped the pan took off the belt and checked group 110 on the vag and no misfires. Tring to understand what was going on I put the belt back on to do another scan and notice the belt clears the tensioner by a hair. 
It seems the tensioner was at its limit and allowed belt slippage. I did check the voltage on the vag and with a meter on the alternator and at the battery but the problem occured at high rpm under load.So i replaced the belt with a slightly shorter one and the misfire codes were resolved. This is one of those things you occasionally read about in forums and in the back of your mind you think that does not happen, but when you eliminate the obvious and have tried everything what seems to be improbable becomes less impossible.