With the dist diconnected from the computer, it goes into limp mode with no timing advance and full rich command. Once the dist is reconnected the computer advances the timing which should increase the rpm. 650 rpm in park is low, 1k is more normal in park. In drive it should idle at 600 to 650. Idle in drive is lower than idle in park due to the load from being in gear. This is why idle adjustments are made in drive.
SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.
2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.
Never argue with an idiot.
They will just drag you down to their level and beat you with experience.