Quote:
Originally Posted by thstone
The SAI is used primarily at start up to reduce emissions when the engine typically runs fairly rich and the cat's may not be up to full operating temp. Use of the SAI leans out the exhaust gas for better emissions.
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Your wording makes it sound like the extra air "dilutes" the exhaust gas mixture, but in fact the extra oxygen causes the unburned fuel to actually burn. It's not "leaning out," that is.