Mitsubishi Repair: high idle, throttle position sensor, eclipse gst

Question
95 eclipse gst 5spd fwd
  the engine was ideling high (around 1100 rpm)and the check engine light was on. it read 0505. so i took the old iac out, cleaned it w/carb spray and inside the throttle bdy, put it back in and it seemed to idle even higher.i ended up putting a new one in. it still idled high and the rpm's surge up and down. i give up.

Answer
Josh,
You mentioned that you ended up putting in a new one.  Are you referring to a new throttle body or the IAC?  If you replaced the IAC, the problem may be the Base Idle Setting Screw (BISS) on the throttle body.  The BISS is a screw on top of the throttle body that is used to set the idle speed.  If the o-ring that goes around the BISS is leaking, that will cause a high idle.  

Though if you ended up getting a new throttle body and an IAC, then there could be an air leak within the Fast Idle Air Valve or even a malfunctioning throttle position sensor.  There are many small components around the throttle body that could cause high idle problem.  You may need to perform a leak-down test to find out if your high idle is being caused by an air leak, or if the problem is within a sensor/eletrical component.  A malfunctioning ECM can also cause this problem as well.
Good luck!