I was going through some old files and this one was easily diagnosed from just the paperwork though the truck left here years ago. 2002 Ford F-150 XL with 4.2 engine and trouble codes stored that indicate lean fuel mixture on both banks.
Important clues are stored in the freeze-frame. The truck is sitting at idle, still warming a cold engine and fuel trims are high.
These engines had a known problem with the seals around the bolts that attach the plenum to the lower intake manifold. While the engine was cold the seals would draw up and allow a vacuum leak. Once warmed up the seals would stop leaking. This is a common problem on many engines with the plenum gaskets allowing this to happen but on the 4.2 it was usually not the actual plenum gasket but the seal at the attaching bolts. The fix was to replace the plenum gasket and attaching bolts. The gasket was readily available at any parts store but to get the updated bolts they had to come from Ford. The updated version was green in color.
You could verify this as the problem by letting the vehicle cool down overnight, start the engine, pull up the short term fuel trims on a scan tool and watch the data while spraying some carb cleaner in the area between the plenum and lower intake. If the vacuum leak was there it would pull in some of the carb spray and you would see the immediate change in the fuel trim.
Kenny@ggauto.repair
