The EBPV will only actuate if it's rather cold out. Once the engine is up to operating temp it never actuates the valve. So seeing as it started acting up while he was driving I'm guessing something else is going on.
If it was stuck shut you should hear the engine choking up from it. Just make sure the EBPV actuator valve is all the back in the pedastel, then unplug the EBPV actuator. This is the little 2 wire connector on the front of the turbo pedastel. If you unplug this then it won't be able to push the valve shut.
Alot of times you will have a EBP related code, but they can be from a few things, like the EBP sensor tube plugged or the EBP sensor not working. You would almost need a scan tool to moniter EBP pressure while it's running to narrow down a EBP issue.
Since your not getting any codes I'd start with checking fuel pressure, then I'd pull all the injector wiring harnesses going into the valve cover and check for melted terminals.