Just re-read your last posts. What caused the EML? Have to get the car scanned with a fault code reader or, ideally, the VAGCOM or VCDS software to work out what's causing the light.
OK so if checking and servicing the valve are all good then you may have a
problem with the vac line running into the top of the valve, possibly a split or insecure fixing at either end. Either of these would stop it from opening properly (or at all) and potentially throw a fault code.
If you're finding that in reverse you're not getting the chatter then I'd have thought that would support the theory that the valve wasn't opening correctly - the vacuum acting on the top of the piston may not have been enough to open it alone but now that the boost is pushing against the bottom of the piston instead of the side then that might have sorted things out a bit.
Incidentally, I wouldn't change anything else on the car until you identify and fix the cause of the EML, otherwise you could end up just confusing the issue.