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...Diagnostic trouble code P0506, defined as "Idle control system RPM lower than expected"....

...But...with this method the pintle doesn't physically move but the ECM gets data from the IAC saying that it DID move. The perfect fake out...


Therein lies the problem , methinks.



The ECU will use the tachometer to measure the engine revs. If it detects no change in engine revs for a given change in IAC servo setting it will set a CEL as it gets to the end of its range of output to the IAC -"maxes out" (failure of the "closed loop" system)

My guess is there would be a predetermined idle revs for hot/cold/aircon/etc type situations programmed in to the ECU, and that the IAC is used to achieve this by increasing the revs from a baseline figure.



You may be right Gary. It depends how much leeway is built into the ECM map. As long as you stay within the map it would work. Once outside it then the CEL comes on.

1998 Sportage - Gone.
2004 Honda Civic Coupe.
2007 Suzuki Grand Vitara - She got it.