Mitsubishi Repair: fast idle-92 expo 2.4 l, throttle position sensor, stop screw

Question
92 expo 2.4 liter developed fast idle (guess about 1100 rpm spontaneously 4 days ago.  I am on small island in Caribbean--no scanning tools--no parts and I have very minimal mechanical experience or ability.  Have read everything I can on net--understand only part of it.  Have sincere mechanic but not real sophisticated.  Here is scoop following his examination:  No vacuum leak found. Disconnected throttle position sensor and made no difference at all in idle.  Adjusted stop screw for throttle cable beneath throttle housing--made no difference and returned it to original positon indicated by paint.  Cleaned carb with carb spray--no differnece.  Claims butterfly is working fine, mechanically.  Adjusted what I suspect is base idle set screw on top rear of (carb or throttle mechanism)--no impact.  I read faulty O ring could leak air around this but screw is inset into body of mechansim with black cap--put finger over opening tight to block off air--no difference.  Throttle cable works fine-is not hung up.  I will be returning to US in 4 days and can bring back parts.  My question:  is his assumption that the problem is the throttle position sensor simply because when he disconnects it there is no change in idle, feasible?  If the problem is the Idle air control (which I have read is sometimes the case, is there a way to determine if it is the IAC or the throttle position sensor? I do apologise for my lack of sophisticaton here, but you have now heard more than I know.  If there is any way you can suggest how we might isolate the problem so that I can bring back the most likely or correct replacement parts, I will surely appreciate it.  We have very limited resources here and it would sure be nice to keep this car running.  Thank you very much!

Answer
Rick,
There are simple ways to test your throttle position sensor and IAC if you have a voltmeter.  Unfortunately, I do not the procedure and tolerances specifically for a 92 Expo.  But you may be able to search around on the internet that will give you general detailed instructions.  Sorry I couldn't be more help.
Good luck!