Q: code po171 already changed spark plugs and ignition coils and was told by Firestone that was what it needed

asked by on

during cold starts and when sitting at stop lights ruff idling begins the code that was given was po171
My car has an automatic transmission.

Code P0171 is set due to a system lean reading. While worn or misfiring plugs or coils can cause the issue, they typically do not. Most common causes would be a mass air flow sensor or even a leaking intake manifold gasket. If the engine is drawing in too much air from a leaking intake gasket for example, this can effect the air/fuel mixture and set a code. Another component not usually suspected with a code P0171 can actually be a cause. The Air Solenoid Control Valve. This valve directs air from the air injection system into the exhaust on cold start and running. This is an attempt to reduce cold start emissions when vehicles pollute the most. From age and carbon build up, the valve can intermittently stick open, causing more air to be injected into the exhaust. The additional air will cause the oxygen sensors located in the exhaust system to give false readings and adjust the air/fuel mixture based on them. This can cause a rough running and check engine light to come on. A certified technician will be able to diagnose the cause of the check engine light and fault code P0171 to find the exact cause.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 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
  1. Home
  2. Questions
  3. code po171 already changed spark plugs and ignition coils and was told by Firestone that was what it needed

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: Failing fan clutch symptoms

What you described is happening is normal cooling fan clutch operation. When you first start the engine the cooling fan clutch will be in the full engaged position and may take a minute for the internal fluid to move back...

Q: I have a 2006 Jeep Grand Cherokee with 19k that has been sitting for 6-7 years , what needs to be done to get it running again?

You will need to start by draining all the fuel and put in new fuel and then see if it starts or the pump and filter assembly may be bad.

Q: Car runs fine but will not go over 45mph the check engine light is not on it was fine until I had to change transmission line

Hi Sandra. Thanks for contacting us today. There are a few different items that could be the root source of your GMC's issues. The most common problem is that the transmission fluid is either low or there is debris trapped...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
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...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...