My initial thought I that if it worked OK when it went to the mechanic, then it should be returned to them to resolve the issue.
It sounds like the timing is out by a tooth when fitting the timing belt.
The easiest way would be to perform some live data logging in VCDS, the actual values to measure escape me at the moment, but I'm sure someone will be along soon to point you in the right direction. If the timing belt is a tooth out, then judging by the TFSI FB page, this happens every so often. The biggest issue is getting the mechanic to agree and fix it as they always swear blind that it cannot be the case.
Otherwise check all your pipes, hoses and other connections are all good. Any vacuum leaks?