Hi,
The fuel trims are controlled by the powertrain control module (PCM) and other sensors. They couldn't have manually adjusted it.
A rich fuel mixture can be caused by a couple of things. For example, excessive fuel pressure due to a regulator issue, a failing fuel injector, or even an engine coolant temperature sensor. By any chance, do you have access to a live data scan tool? If you do, when the engine is cold, check the coolant temperature signal to confirm it is close to the ambient temperature.
Also, let me know what the short-term fuel trims are at idle and the engine at operating temperature.
Let me know if this is something you can do or have done.
Take care,
joe
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Friday, May 12th, 2023 AT 9:06 PM