could be a throttle position sensor fault or ecu fault perhaps.

The TPS (on mfi) has 3 positions
Throttle closed
In between open and closed
and full throttle

If the ecu thinks the throttle is closed you maybe running very lean etc.

Im not sure if this will actually cause the symptoms you've got though. Like no boost at any thing other than WOT.... i would imaging you car would detonate/stutter as well.

So like S1 John says it could be shite rich.

Rob,