Ruminations:

Note that the lambda sensor is out of the loop until the engine warms up. If it then is indicating rich at idle, the ECU will attempt to correct this by adjusting the EHA. If still out of range, I believe it will attempt to add more air via the idle control valve. Note, though, that if you get a hunting behavior in the idle speed, you may have a bad airflow meter pot. This would indicate falsely a need for enrichment (bad spot on pot causing a sudden increase in output voltage), followed by a response from the EHA, and then an increase in idle speed to compensate for the rich mixture that results. Then the pot is no longer in the 'bad' spot, and the idle settles back down.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7