Q: Rough idle after replacing Mass Air Flow Sensor - trouble codes P0171 and P0102

asked by on October 28, 2016

Was having problems with car turning off at red light or when coming to a stop. Check engine light indicated mass air flow sensor. Replaced air filter and maf sensor. Problems with vehicle turning off seemed to go away but now I have a rough Idle. Car will drop below 1000 rpms and then rev back up to over 1500 like it wants to shut off. Idle problems seem to go away when maf sensor is disconnected. Car throwing codes p0171 and p0102. Where should I go from here?

My car has 190000 miles.
My car has a manual transmission.

The P0171 refers to a possible lack of fuel pressure, a leak in the intake air system, or a possible vacuum leak. The P0102 also leans towards a leak in the intake air system. It is possible that there is a problem with a BARO (barometric pressure) sensor that is reading faulty. Its purpose is to measure atmospheric pressure, the amount of air entering the engine, and supply the ECM with a calculated reading that allows the engine to make corrections accordingly.

If the BARO sensors readings are off, the supplied amount of fuel will be incorrect, and can therefore cause running issues. I would first check all of the intake plumbing to be sure it is all seated and tight, and then test the BARO sensor for correct function.

I recommend having a certified mechanic, such as one from YourMechanic, come to your location to determine why your car is idling rough and if the barometric sensor needs replacing.

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