Vehicle had fault codes for lean fuel system, both banks.

This indicates a problem affecting the entire engine.

With fuel trim faults, freeze frame data is a great starting point. Freeze frame data indicates fault codes set at idle.

Monitoring fuel trim during a test drive confirmed the vehicle was lean at idle. Note the graphs below indicate lean at idle. Once the engine RPM is raised from idle to 2500 rpm (in PARK) the fuel system is no longer lean. A vacuum leak can be detected this was. As the amount of unmetered air is larger (or comparable) compared to metered air. Once the RPM is raised the metered air amount becomes greater than the unmetered amount (vacuum leak).

After this I spoke to the mechanic who was working on the Windstar. He stated the same fault codes were present last month. He found a leaking intake manifold and a TSB. Therefore he replaced the front valve cover and intake manifold profile gaskets.

I quickly checked over his work. Everything looked in place. The only spot that propane could influence fuel control was at the intake manifold runner control bushing. I found this to be normal as all 3.8 intakes will have some level of leak here. New lower intake manifold does not remedy the leak.

I looked over the TSB and asked if he performed a needed PCM updated. They had not.

Next up I reprogrammed the PCM.

After the PCM software update I test drove the vehicle and confirmed it was now in proper fuel control. A second test drive confirmed the same result with no fault codes.

The shop was half way there. They performed almost all the needed repairs. A simple software update and they were done. With computers controlling almmost every function on late model vehicles it is always smart to check if software levels are up to date when performing repairs.