The engine can't run without air, air control controls the engine speed. That is done at idle with mechanical restrictions and the idle control valve. The most likely causes of excess air are a throttle valve prevented from closing to the idle position (linkage problem) or an air leak bypassing the idle control valve.

Another possibility is the ECU increasing the idle control valve opening due to an excessively rich mixture.

Steve

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