P1 turbo uses a check valve on the turbo inlet neck for the crankcase vent. That check valve is supposed to be sucked closed idling and when off idle and boost builds the check valve for intake closes and this one opens to let vapors go through turbo and intercooler and back through throttle. If the...

If following helps, this is emission code 2 diagram:

The evaporator pipe pn 30751987 (item #1) is apparently used in two styles, emission code 2, and code 4/5.

FWIW, here is a diagram of code 4/5: