Skip the auto shop - Our mechanics make house calls

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

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  • Home
  • Questions
  • Rough idle after replacing Mass Air Flow Sensor - trouble codes P0171 and P0102

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Fanclutch

Hi Joseph. Thanks for contacting us today about your VW Passat's fan clutch issue. Usually the fan clutch is removed after you remove the assembly as you've indicated. One of the best tools you can use to learn how to...

Q: I have a coolant issue I have replaced the radiator the fan and the thermostat but when my car is running for 15 min coolant comes

Overheating can be caused by a number of things such as low coolant levels, a faulty thermostat, a clogged radiator or a failing coolant fan switch. As you may know the coolant fan switch helps to maintain the proper coolant...

Q: Instrument panel lights are on - codes P0102, P0069

Both of these sensors have to do with sending air mass and pressure information to the engine computer. It is likely you have a vacuum leak or these sensors are starting to fail and are offering the engine computer false...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...