Engine Idle Problem 1989 Lincoln Town Car

Hello. My question is for my 1989 Lincoln Town Car. When I
start the car it revs high like normal for about 20 seconds,
then the engine rev gets very low and sounds and feels like
it is about to stall out. Like the engine is not putting out
enough to run the engine. The IAC valve is fresh, I loosened
the screw so the air intake butterfly valve is open more.
Here is the thing. I'll step on the gas slightly so it revs
normal, drive it and when inarrkve wherever and put the car
in park after driving, the idle is fine...sounds normal. It Is
only with the initial start up that it wants to try and stall or
almost stall.