Lean codes are usually due to a vacuum leak. Sometimes improper EGR flow.
Depends on which code(s) have been set or are pending. Check your longterm fuel trims...
Steve
98 Contour SE Sport 2.5 Duratec ATX The wifey's car
89 Taurus SHO - 246K miles
94 SHO ATX - 190K
1997 F-150 5.4L ATX - The Workhorse 150K.
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