Mitsubishi Repair: 92 Eclipse 2L DOHC Cold Idle Surge, air fuel mixture, harness test

Question
My 1992 Mit Eclipse 2L DOHC 5 spd has a second generation ISC motor.  A few months ago, this problem arose:  When engine cold (and ambient temp below, say, 70 degrees F), idle starts at about 12-1500 rpm, then slowly rised to about 2000 rpm, then oscillates between 1500 and 1800 rpm at about one cycle per second, until engine begins to warm up, then idle slows and becomes and stays normal, including properly reacting to loads.  If I remove connection to Idle Position Switch DURING oscillation, oscillaton stops and engine idle normally-however, engine performance if driving with IPS disconnected is less than ideal.  I've tested IPS and harness, and both OK.  I've tested ISC motor warm, and it tests good.  Haven't tested it cold.  AFS tests good.  Temp Sensor and harness test good.  No Codes for any of the foregoing.  SECOND PROBLEM:  For a long time I've gotten a Code 11, OXYGEN SENSOR.  O2 sensor replaced, harness and sensor test good, but still get code 11.  Even Mit dealers, those few who will even look at it, can't tell me a fix.  
I am primarily concerned now about COLD IDLE SURGE.  Any ideas?

Answer
Eddie,
Your cold idle surge may be caused by a problem with your car's computer.  Read this article for more information:
http://www.90gsx.com/eclipse/cap/caps.htm

The ECU controls the idle speed and if the speed levels off when connection is removed, that means the ECU was telling the idle to oscillate.  This is not a cut and dry conclusion to think your ECU is the overall cause, but you should check your ECU.  You should also check your PCV valve, EGR valve and your FIAV (fast idle air valve) if you haven't already.

For your O2 issue, that can occur if your air/fuel mixture is too rich.  The O2 sensor is pretty sensitive and can have false detections.  You may have luck running a tank full of premium gas and bottle of fuel system cleaner.
Good luck!