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AFR changes when idle.
apparently, my afr became lean prior to starting the car after parking the car for awhile.
why is this happening?
Have you tuned the coolant temp compenstion? Normally as the engine is cold, it will need extra fuel just to achieve the target AFR. The coolant temp compensation will generally add fuel while the engine is below the operating temp. You have to first tune the AFR under normal warm conditions, then on a morning when you start it cold, you adjust the compensation for each temperature as the engine warms up.