99 Town Car; idle is erratic only in Park and Neutral

[L3DStech]

1999 Lincoln Town Car Cartier. 191k miles. As long as the transmission is in Drive or Reverse the RPM is steady at around 625.
When its shifted into Park or Neutral, the RPM fluctuates from 625 to 1300. There are no DTCs.
Previous repairs-
Replacement attempt of the heater core. Steering column was lowered to the floor and the dash was halfway removed.
Transmission filter and fluid change (including draining the torque converter).
Intake manifold replaced as well as both valve cover gaskets.

This symptom started after the dash and steering column were disturbed. Is it possible that I missed plugging in a sensor?
I will be very grateful for any help.

Craig

 

[L3DStech]

UPDATED. More info

So, I apologize for not updating this thread sooner. The added info is that the A/C must be on for the idle to be erratic in Park and Neutral. Maybe now someone will be able to help me with this problem. Thanks again, Craig