Alanmitsu, those are good points. The dealer tech came back today and repaired air flow sensor wiring (it wasn't broken, but the insulation was pretty ragged) and then installed a new air flow sensor, but no help. As you mentioned, he also said it wouldn't throw a code. I had ordered and we replaced the LP filter at the lock off, still no help. He thinks we should replace the injector- so I'm gonna check with the customer tomorrow.
Tell me more about the assist injector- I know this only fires under high load/ high RPM. Can it leak/ bypass?