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What's the year, model and engine size of your vehicle?
DTC P0174 Bank Lean can set for a few reasons such as an air leak after the MAF sensor, engine vacuum leaks, low fuel pressure, a faulty MAF sensor, leaking EGR, cam timing or an exhaust leak before the O2 sensor. If the fuel pressure is good you should check for vacuum leaks by spraying some carb cleaner around the intake and see if the engine rpm changes or engine idle changes. If you have a scanner you should monitor the fuel trims to see what they are at. Anything above 7% usually indicates a vacuum leak.
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