Hi Matt,

It never hurts to think, once some thought has gone into the process, the information normally stays there to be called upon at a later date.

>>> My understanding is that the flap aids smooth engine shutdown, by closing.<<<

No sir, not on this vehicle, it is used to control the manifold pressure under certain operating conditions for the purpose of EGR flow.

A good place to start may be by checking the VAC supply, followed by actuator tests, followed by EGR operation AMM readings and validating the boost pressure sensor.

Regards Mark