Q: RPMs erratic during idling, Check Engine Light on, P0174 code

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The RPMs are fluctuating erratically while the truck idles. It is similar to the AC compressor turning on and off. The dash is showing the check engine light on too. The truck has been getting very low gas mileage, like 13-16 MPG. After having the codes read, the P0174 error code appeared. The repairs done on the truck so far include the replacement of the oxygen sensors, gas cap and MAF. Also, the cleaner was added into the fuel injection system. What is causing this and what does the error code indicate? What kind of repairs are necessary on the truck?

Hello. The P0174 code deals with the truck running lean. That means that the PCM is restricting fuel to the injectors. This is usually caused by a vacuum leak in the engine. There could be a leaking intake gasket, or a broken or disconnected vacuum hose. The may cause the truck to run lean and have an erratic idle. I would recommend that you have the intake and vacuum lines to the car checked for leaks and breaks. Have a certified technician, like one from YourMechanic, diagnose the idling issue and assist you with repair.

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