P0171 P0174 Check Engine Light CEL

[andrewwynn]

https://www.motor.com/magazine-summa...agnostic-tool/

A very good article.

Suggesting a stuck open purge valve.

If the hose is soft enough you can pinch it shut with a couple pieces of wood and a locking pliers (or pick up the hose pinching pliers made for this job)

Purge valve or dirty / sticky injector.

Have you run injector cleaner? This model engine uses math to estimate the amount of gas per intake stroke. If the fuel pressure is off that's one way for the math to be wrong but when dirty the injectors will shoot less fuel thank designed so fuel trims will have to rise to compensate.

Since there's no feedback loop for How much actually comes out except O₂ sensor and the ECU assumes the injectors are perfect out blames the intake air.

One other test for stuck open valve: I wonder if there's a path to the fuel tank from the purge line a smoke test would feed back out the fuel fill. I can't remember the exact plumbing out might only go into the charcoal canister.