idle rpm

my 1992 318 dakota seems to be idle really low. right now its start up idle is at 400 rpm. when it gets warmed up after bout 15-20min, its startd to idle down to around 100-150 rpm. Im in the process of changing the fuel filter, hopeing it gets more fuel bringing up the idle rpm.
If anyone else has had this problem let me know, Thanks.

make sure throttle body bore is clean the pcm knows how much air is supposed to enter there and after a while the bore gets gummed up and restricts the air flow and the pcm doesn't know this and it only alows a certain program for the ais motor
wich doesn't compensate for this restriction at the bore a good carb cleaner and toothbrush will do