Cause
Failed cold start injector
On systems that use one, the extra injector that adds fuel only during a cold start. It runs for seconds and only below a temperature threshold, which is precisely what makes it hard to test — by the time anything is connected it is not supposed to operate.
Its failure is a cold-start complaint that vanishes entirely once warm. Long cranking, a stumble in the first seconds, or a stall immediately after firing — with an engine that is faultless for the rest of the day. A vehicle that starts badly only on the first attempt of the morning is describing this, and the owner has often stopped mentioning it.
Leaking is the other direction and the more damaging one. An injector that passes when it should be closed adds fuel continuously, so the engine runs rich when warm and can wash oil from the bores. Check it both ways: that it delivers when commanded cold, and that it seals when it is not.
Typically a moderate job.
Codes this can cause (2)
Codes where this is a likely explanation first, rather than merely a possible one.
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