Download ISSUE Some 2001-2003 F-150, 2004 F-150 Heritage and 2001-2003 E-150/250 vehicles equipped with a 4.2L engine may exhibit the malfunction indicator lamp (MIL) on with diagnostic trouble codes (DTCs) P1131 and/or P1151 (system too lean bank 1 or 2). This condition may be due to leaking isolator bolts/port gaskets in the upper-to-lower intake manifold mounting area. This condition is sometimes intermittent and may not be apparent on a warmed-up engine. ACTION Refer to the following Service Procedure. SERVICE PROCEDURE NOTE THIS CONDITION COULD ALSO BE DUE TO WARM AMBIENT TEMPERATURES AND THE USE OF WINTER GRADE FUELS WHICH HAVE VERY HIGH VOLATILITY AND MAY BOIL IN THE FUEL LINES (VAPOR LOCK) DURING A SHORT HOT SOAK. OXYGENATED FUELS WILL AGGRAVATE THIS CONDITION. IF NON-OXYGENATED FUEL IS NOT AVAILABLE, USE MID/HIGH OCTANE FUELS WHICH HAVE LOWER VOLATILITY AND MAY HELP ALLEVIATE THE CONDITION.