The underlying problem was the Idle Air Intake Control Solenoid. The following paragraphs are for any other poor sod that is using a keyword search for this problem.
Our 2001 EJ 201 2.0 Impreza had a defective Idle Air Intake Control Solenoid. Performance wise the car behaved perfectly normal EXCEPT:
- Check Engine Light was intermittently illuminated.
- Performance was lousy when said light was lit.
- There was absolutely no pattern to when the light came on.
During "Light On" and "Light Off" moments it idled perfectly.
We had replaced the IAT / MAP Sensor and TPS as well as cleaning the MAF and Throttle Body. No change. However, I found that the Idle Air Intake Control Solenoid had adjustment so I screwed the plunger out. This changed the frequency of the fault, thus leading us to the conclusion that this component was the problem. Replaced with a new one (Part A33-661) and "Bingo", back to normal. BEWARE! In our case this fault threw the following codes:
- Code 0112 Intake Air Temperature Circuit Malfunction.
- Code 1112 Atmospheric Pressure Sensor Circuit Range / Performance.
- Code 0121 Throttle Position Sensor Circuit Range / Performance - High Input.
As you can see, THERE WAS NO CODE RELATING TO THIS COMPONENT.
Furthermore, when current was applied to the solenoid it appeared to work correctly.
Anyway, some months later and the problem is finally solved.
Thanks to all who offered their input and counsel. AND HAPPY EASTER!!