Your idle will be lowest in gear with the engine up to temp. Just a little food for thought, typically when we test it's in Park. Since the voltage isn't dropping, that leads you to start speculating at the BCM/IP. The IP is more common from what I've seen than the BCM.
FWIW I have flipped a few Regals and once pickued up a 98 where the woman told me, "It's possessed and the gauges work backwards" Upon getting it running the low oil pressure light was blinking, the temp was indeed reading backwards and overall many issues. A simple cluster swap and the car was great. Oil pressure tested at 70psi with a mechanical gauge.
