At cold start the engine uses adaptive and fixed parameters to start the engine and then keep it running. (Adaptive being things like IAC position for given engine and air inlet temp for a desired rpm) (fixed being things like fuel and spark maps).

As soon as the ECU sees a valid input from the front O2 sensor (voltage creeps up to around .85vdc) it goes closed loop and starts the enrichment warmup process where you will see the O2 voltage cycling high low. Starting around 10:1af and slowly going up to 14.7:1.

Until the engine hits around 130-140 it’s running 13:1 or less and that makes more power.


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