Code P0171 rough idle and idle surging

Hi,

What parts have already been replaced? Also, a lean mixture can be the result of several different things. However, the most common are low fuel pressure or an engine vacuum leak. I have even seen an exhaust manifold (pre catalytic converter) leak cause it. Have you noticed any exhaust issues? It could actually sound like a ticking.

If not, the next thing I suggest is to check for engine vacuum leaks and fuel pressure. Here are two links to help with that process:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If you have already tried this, let me know. Also, let me know if you have a live data scan tool. There are several other things that can be checked such as a faulty engine coolant temperature sensor, air intake temp sensor, mass air flow sensor and so on.

The attached pic indicates the manufacturer's specs for fuel pressure.

Let me know.

Joe

Hi,

The P0302 indicates a misfire on cylinder 2. That is likely what you feel. Since there is a lean mixture, that could be the cause. Can you do me a favor? Take the live data scanner and check short term fuel trims and the oxygen sensor readings. Let me know what you find. Also, does the ticking sound go away after the engine warms up? Have you confirmed there are no vacuum leaks?

Let me know.

Joe

Let me know what you find. Also, I assume the ticking is with the engine off, so that isn't an exhaust leak. I have a feeling we have a fuel pressure issue.

Let me know.
Joe

Hi,

The O2 sensor is reacting properly. The STFT1 is really high, indicating the computer is trying to add fuel. STFT2 is right on. How does your scan tool differentiate or what does it differentiate between 1 and 2?

Hi,

Yes. In a perfect world, the fuel trims would be at 0. It's normal for them to fluctuate a bit. The one that is at 15 indicates it's trying to compensate by adding fuel to the mixture. If that number was negative (for example -15) that would indicate it is trying to limit the fuel. So the idea that it is +15 tells me it is trying to add fuel because there is too much air resulting from a leak or low fuel pressure.

I hope that makes sense. Please feel free to ask any questions. If I can answer them, I will.

Joe

It would be in the upper + (positive) range. Basically, where it is now. Under normal conditions, at an idle I would expect to see the STFT's to be changing between negative and positive 2-5%. It's staying near +15%.

Let me know if you have other questions.

Take care,
Joe

Hi,

Basically for a fuel pressure test, you need a fuel pressure gauge. Here is a link that shows how that is done. Most auto parts stores will lend/rent the gauge to you.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here is a link that explains how to locate a vacuum leak:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know what you find.

Joe

If you are referring to when you first press the throttle to rev the engine, that is expected. Any luck checking fuel pressure?

Joe

Let me know what you find. Also, anytime I hear surgery, it isn't good. I hope you are well and everything goes smoothly for you.

Take care,
Joe