Cause
Faulty air cleaner inlet actuator
The actuator that switches an intake between air sources — typically a cold outside inlet and a warm one drawn from near the exhaust manifold. The system exists to keep intake air within a workable temperature band, warming it for driveability when cold and taking cold, denser air when not.
A failure leaves the intake stuck on one source, and which one decides the season. Stuck on the warm source, the engine draws hot air permanently, which costs power and can trip intake temperature rationality checks in summer. Stuck on cold, cold-weather driveability suffers and icing becomes possible in the throttle body.
The actuators are usually vacuum-operated on older systems and electric on newer ones, and both fail at the same points: a perished vacuum line or diaphragm, or a seized flap. Check the flap moves freely by hand before condemning the actuator — the flap sits in the airflow collecting dust and its pivot seizes, which is a free thing to rule out.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (3)
Codes where this is a likely explanation first, rather than merely a possible one.
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