Too lean at idle does point kind of to PCV.
You could, I have no idea if this is the done thing you do so at your own risk and if anybody else says no then its no but its what I did, take the engine cover off and remove the PCV connection pipe from the PCV. Its the one that sits in between the PCV and the intake manifold. I just got some Duck tape and placed it over the PCV outlet to intake and refitted the pipe back on. You have effectively sealed off any leaks to the inlet which is what a PCV fault causes.
Put the cover back on and everything else.
Start the engine and let it idle.
Turn off, plug VCDS in and clear all your faults.
Drive about or whatever and see if the Lambda fault comes back on.
THERE IS A CHANCE I COULD GET SHOT DOWN FOR THIS PROCEDURE BUT, NOT BEING A BILLY BIG B******S, I CAN WORK THINGS OUT FOR MYSELF AND KNOW THE RISKS. IF YOU CHOOSE TO TRY IT DO SO AT YOUR OWN RISK. I WILL NOT BE HELD RESPONSIBLE FOR A BLOWN ENGINE OR WORSE A TRIP TO HOSPITAL. IT WORKED FOR ME TO DIAGNOSE A FAULT I HAD.
If it works get on to Dubtek and buy a PCV deletion kit for £70 or even better a BSH catchcan.