High cold idle is usually the temp sensors, throttle body fuel leaks and or vacuum leaks. I don't like the idea of re-setting the throttle plate, that may have something to do with it too. I would pull the codes if any and then disconnect the negative battery cable to clear the ECM, take the car for a drive over 35mph to re-learn the idle.
Skybax posted a procedure on how to re-set your throttle body plate for a V-6, you already messed with it on your Duke, you haven't got much to lose now, might help.http://www.fiero.nl/forum/A...050410-2-057305.html
Try to beg borrow a scanner to see what's up with the sensors, some auto parts stores have tool loaner programs, even a small multi-meter on those temp sensors might uncover the difficulties.
I will ask what year your 2.5 is because the older ones still needed to have the timing set too.
[This message has been edited by jetman (edited 02-26-2008).]