engine light

[CoastieCosta567]

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[SilverBullet75]

I just did a Google search of P0171:

NOTE: This is "universal" info on the code...

System Too Lean - Bank 1

The following is an overview of P0171 check engine light code possible causes.

Fuel System:

Leaking or faulty fuel pressure regulator
Plugged or dirty fuel filter or lines
Fuel pump weak or defective check valve
Injectors leaking or faulty
Low fuel pressure or running out of fuel
Leaking EVAP system components
Faulty FRP (Fuel Rail Pressure Sensor)

Air Intake System

Vacuum leaks
Contaminated, damaged or faulty Mass Air Flow sensor
PCV valve leak or stuck open
Air induction turbulance caused by wrong filter
Oil dipstick not seated
Air leaks after the Mass Air Flow Sensor (MAF)
Oil coated aftermarket air filter

Exhaust System

Any exhaust leak before or near the oxygen sensors

EGR System

Vacuum line disconnected from EGR System Module (ESM)
EGR valve, tube or gasket leak
EGR vacuum regulator valve leaking

Secondary Air Injection System

Mechanically stuck secondary air injection valve

[Y33TREKker]

How many miles currently on your VX, and when was last time you changed fuel filter, air filter, etc?

[Daly]

86k on vx. Checked for vaccum leaks.
Going to change the air filter, gas filter, pcv valve, ignition coil (expensive little buggers) as one is pretty surely bad, and spark plugs.
If they don't fix it, will move on to a couple of the other possibilites.
Certainly a lot of choices to fix, would have been nice if the code was a bit more specific.
I was surprised at the prices of the replacement parts. Went through Merlin of course. MAV, O2 sensors, coils all over a hundred bucks each. Even the spark plugs were expensive.