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Engine misfire (rough idle, power loss) and system too lean codes. Tried new coils and plugs, no apparent vac leak. PLEASE HELP

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New member
Jun 20, 2022
My Lincoln
2003 Navigator
For months I’ve had random misfire problems and engine too lean codes. I changed coils and plugs and it was better for a day before engine light came back on. Rough idle, low power, mpg loss, light will flash when trying to accelerate at higher speeds. Changed PCV valve and hoses after mechanic found small vac leak. STILL same symptoms persist. Mechanic supposedly checked MAF sensor and other easily accessible potential suspects. Idk what to do. Is it wiring to coils? Fuel injectors? Fuel filter? 2 mechanics so far have tried and failed to find solution.

2003 Navigator 2WD 160,000m 5.4L


Junior Member
Aug 12, 2005
Phoenix, AZ 85008-1418
Check for vacuum leaks

If it has over 100,000 miles replace all of the O2 sensors