i have a 1989 300te that idles low,about constant 575 rpm when warmed and it will stall mostly as one is slowing to a stop.
i have another 89 300te that works good,holds a steady 700-750 rpm and never stalls. so out of the good one i have exchanged the computer behind battery,swaped the ovp,exchanged the idle control valve -,fuel pump relay and all the exchanged parts kept the good one good and didnt change the stalling one at all.
in addition i have checked the throttle idle switch,and the decel switch.
absoutley about to throw in the towel, on the good car the only difference i can see is that the voltage across the idle control valve input starts from about 9-10 vdc when cold and decreases to say 5.8 dc when warmed to 80c and does not change to increase the idle speed when placed in gear or loading down with the a/c. the good one seems to start with a little higher value when cold say 10-12 dc across the idle control valve but it will regulate to a higher value when the tranny is selected to a gear and a/c will also cause the idle valve to be increased,resulting in a good control of 700-750 rpm.
i am not sure how the full control is done but i did check the vacuum and it is 17 in at low rpm and goes up to 20 at fast(about 2000 rpm)
i did test the ezl ignition vac and it held 15 on the mitty mac,
any suggestions would surely be appreciated
larry perkins lou ky