Mitsubishi Repair: Idle surging problems, throttle body, probable cause

Question
I have a 1992 Montero automatic with 150k miles.  Just depending on the position of the moon is what it will idle at. Either at 2500 to 3000 rpm's, or 250 rpm's.  Replaced the computer 2 months ago, had the idle set, and checked for codes (no codes were found).  Is my only choice to replace the IAC?

Answer
Kellie,
The IAC is the most probable cause to your erratic idling.  If you notice your idle is erratic even after your engine is at normal operating temperature, then odds are your IAC needs to be replaced.  But if you have the ability and the time, I'd recommend removing your throttle body and cleaning it thoroughly with carborator cleaner.  A clean throttle body can also help with some idle problems.
Good luck!