Before authorizing that repair, I strongly recommend the following:
* Get a second opinion: Take your Windstar to a different reputable mechanic, ideally one specializing in Ford vehicles. Explain the code and the dealer's diagnosis. A second opinion can confirm the diagnosis or point to another, more cost-effective solution.
* Thorough vacuum leak check: A lean code indicates the engine is getting less air than the computer expects. A mechanic should perform a thorough inspection for vacuum leaks, which could be anywhere in the intake system (including, but not limited to, the throttle body O-rings). This often involves using a smoke machine to visualize the leak.
* Check the Mass Airflow Sensor (MAF) sensor: A faulty MAF sensor can also cause a lean code. It measures the amount of air entering the engine; if it's malfunctioning, the computer's fuel calculations will be off. Cleaning the MAF sensor (carefully, with MAF sensor cleaner) is often a quick and inexpensive first step.
* Inspect the fuel system: While less likely, problems with the fuel injectors, fuel pressure regulator, or fuel pump can also lead to a lean condition.
Why $400 might be too high for just O-rings: Replacing O-rings is usually a relatively straightforward repair. The cost should primarily be labor, and unless the throttle body is incredibly difficult to access on this model (which I don't know for sure), $400 seems excessive. The price may include other work not clearly explained.
In summary, don't rush into the $400 repair. Get multiple opinions and a thorough diagnostic check to pinpoint the actual cause of the lean code before committing to any expensive repairs. The problem might be something much simpler and cheaper to fix.
