On the P59, does the PCM determine the status of in gear vs park/neutral based on the PNP signal from the PIM, or does it use PRNDL status?
I'm dealing with a swapped vehicle running a 2004 GTO harness and PCM. There's no PNP switch wired up, and the PRNDL Status always says D4. I'm pretty sure the starter doesn't get permission from the PCM either. The problem I am having is when shifting from park or neutral to reverse or drive, the IAC doesn't instantly adjust and the engine bogs. Sometimes it will die. Normally, you can see the desired idle airflow jump immediately when shifting into gear. On this vehicle, desired idle air only goes up when the idle speed tanks until it finally adjusts up to desired. If you shift back into neutral, it slowly drops the idle air by 0.4 lb/min instead of instantly.
If a PIM is required to tell the PCM the difference, then I might be better off switching this thing to a F-body PCM since those use a direct signal to the PCM for park/neutral. If PRNDL status is the determination, we can just wire up a PNP switch. I just don't want to waste time doing one or the other.