Cause
Collapsed intake duct
An intake duct that collapses under the vacuum of full throttle. The duct is clear at rest and closes when it matters, which is why this survives every inspection on a stationary engine — the fault only exists under load.
The symptom is a severe power limit at full throttle with a normal idle, and airflow falling far short of what the module expects. Perished, softened or previously kinked ducting is the cause, along with a duct that has lost its internal support ring. Watch the duct while the engine is revved under load, or check for a restriction upstream — a heavily blocked air filter creates the vacuum that collapses a marginal duct, so the two often arrive together and replacing only the duct leaves the cause.
Typically an easy fix. Often worth checking before paying anyone to look.
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