Cause
Carbon fouling of air assist passages
The fine passages carrying assist air to the injectors, fouled so atomisation is lost. Air assistance exists to break fuel into a finer mist when the engine is cold, and the passages doing it are small enough to close with the deposits every intake accumulates.
So the fault is a cold-running complaint that disappears once warm — rough idle, smoke and stalling in the first minute, with an engine that is faultless by the time it reaches a workshop. The control valve is usually blamed and is usually fine: command it and confirm air actually reaches the injector, because a valve that operates correctly into a blocked passage produces the identical code.
Typically a moderate job.
Codes this can cause (1)
Codes where this is a likely explanation first, rather than merely a possible one.
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