420A Bad Gas Mileage on a cold engine

[DiamondStarMotors]

If I let the engine warm up before I go driving my gas mileage is fine, but if I just hop in and go, my mileage isn't very good until the engine is at operating temperature.

TL;DR I only get good gas mileage when the engine is warm.

 

[andrew k]

computer runs in closed loop until the engine and primary o2 sensor is warm. once it exits closed loop it will rely on data from the primary o2 sensor for proper a/f ratios. no check engine lights correct?

 

[DiamondStarMotors]

no cel. I use to have a coolant light I believe, it randomly went away though a month or so back.