Since it will start up and rev to 2000 rpms, it sounds like you're getting spark. Metering throttle body cleaner in to see if you can keep it running would be an interesting test, assuming you do not have a fuel pressure tester.
It sounds like you might have a vacuum leak which could explain why it revs up and why it won't act up in the warm, heated shop. Maybe if they left the car outside overnight and tried it first
thing in the morning they could experience the issue.
If you can get it to remain running when metering cleaner in though, that would suggest a fuel issue. Also have you tried holding the throttle slightly open to see if it will stay running with the throttle open part way? If so, then it may be an issue with the Idle Air Control (IAC) servo.
-Rod