Try the forum search feature, icon upper right this page, maybe there’s been some comments here about stuck injectors on VW’s. I don’t recall that being discussed though. From the posts we get here, VW’s (excepting their 70’s K-Jetronic CIS versions) seem to be plagued by systematic electrical system problems more than fuel system problems. Have you tried replacing the fuel filter? If not, worth a try and it will give your shop a chance to see if there’s any grit in the fuel.