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Q: Check Engine Light with P0174 code

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Check engine light came on last week. Car was running ok, but it needed to be checked. Had code pulled and it was P0174. I changed the PCV and cleaned the MAF with MAF cleaner. The next day after, the car had rough idle start and very sluggish acceleration. The symptoms do improve after the car warms up. Mpg is noticeably worse

My car has 198000 miles.
My car has a manual transmission.

A: As you know, this code relates to a lean fu...

As you know, this code relates to a lean fuel condition which can be caused by many different things, some of which you have already addressed. The oxygen sensors, which are part of your emissions system, read exhaust gases to determine whether or not the appropriate amount of oxygen is present in the exhaust. Based upon this reading, this information is relayed to the car's ECU which then makes a determination as to whether or not to add more or less fuel to the engine. When too much or too little oxygen is present, this will cause check engine light to come on.

Too much oxygen may be present in the exhaust gas due to things like an exhaust leak, a vacuum leak, a faulty mass air flow sensor (causing a lean fuel condition) or faulty fuel injectors.

Too little oxygen may be present in the exhaust gas may be caused by things like a clogged air filter, a failing mass air flow sensor (causing too much fuel to be introduced to the motor), bad fuel injectors, or a clogged catalytic converter.

When the O2 sensor is not working properly, this will cause false readings to be relayed to the computer causing inaccurate adjustments to be made to the intake and fuel system in your engine. I would suggest having an expert from YourMechanic come to your home to diagnose the cause of the Check Engine Light in person so this gets repaired correctly.

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