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Q:

check engine light on on 1999 Ford F-150

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
code p171 bank 1 too lean. what should i do to fix it?
(1) Answer
The 2 things i would do first is have someone check for vacuum leaks
with a smoke machine.
And also have the MAP sensor cleaned.
Reset the engine light and test drive it.

Sometime a collapsed vacuum hose will not show up with a smoke machine
because the smoke pushes pressure in the hose.
Have someone check all hose with a good bright flash or drop light.