I wouldn't hesitate to take it back to the shop AND WAIT. Make it clear you are going to wait for it to be checked for a loose wire or vacuum line. If you just drop it off, you might have to wait weeks. I like sitting in their office or waiting room where I can chat with other people looking for service. They tend to deal with you faster if you make it known you'll be hanging around. At one dealer that I dealt with I sat in their waiting room with a home made button that said 'Third service trip for same repair.' The owner happened through the area, saw the button and read the riot act to the service manager. It pays to advertise!
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI