OBD codes P0171 and P0441 plus surging idle

The wife's mk2 VRS TFSI has started surging at idle - typically it'll sit at 700ish, then ramp up to about 2000 for a few seconds, then back to 700 for a few seconds and repeat. At around the same time that this started, the MIL came on, initially showing P0171 (mixture too lean) then later also P0441 (Evaporative Emission Control System Incorrect Purge Flow).

I know the PCV valve can cause the former but can it also cause the latter? The valve doesn't appear to have failed in the normal way in that it's still sealing to pressure from the intake manifold side; however, there's a hiss coming from it for a short time after the engine is switched off which stops if I put my finger over the little hole in the side of the body (I can't tell if it's also hissing while the engine is running). Is this hissing normal?

If it isn't the PCV valve, what's next to check? The hoses around the charcoal cansiter all look fine as far as I can tell.

Edited 3 August, 201510 yr by kambites