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

I have replaced the PCV valve, spark plugs, ignition coils, fuel injectors. cleaned the MAP and MAF sensors and the throttle plate. There has always has been a ticking noise that has went on when you turn the key into the on position, and I do have a live data scan tool. And I haven’t tried getting a fuel pressure reading.

Tried to get a fuel pressure reading, but everyone was booked up through the week and I have no idea what else to do.

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

Alright I will. The ticking sound is then you turn the key into the on position and I have confirmed that there are no vacuum leaks.

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

This is when I ran live data, all of the fuel trims are in there. The long term fuel trim doesn’t budge, but the short term jumps a lot.

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?

I don’t really know, that question sort of just stumped me, I’m sorry. But you say it’s trying to add fuel so that would mean there’s too much air?

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

I understand, so what would it turn out to be if there was, for example, a line that had a hole and was pulling in air?

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

Thank you Joe, and I got one more question, what would I need to get to test if there is a leak in the air system and in the fuel system?

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

I will, thank you Joe.

I went over every hose that leads to the intake or is attached to it, and it sucked in none of the carburetor cleaner. And I just did a live data scan, when I brung the rpms up both STFTs went into the positives, I don’t know if that makes it more confusing or a lot easier to recognize

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

Joe

I haven’t been able to check it yet. I’m going to go get a kit tomorrow for it and yeah, I’ve just been pressed on figuring everything out before I go into surgery.

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

Thank you, and when I tried doing the fuel pressure, I kept having leaks, and when I primed the pump I took the line off and it didn’t come out like it had pressure in it.

There was no pressure from the fuel pump?

So, I took it to a shop where they looked over everything, and it turns out my MAF is shot.

I just read over everything we talked about. In my mind, the MAF was already replaced but I saw you cleaned it. I am so, so, so sorry I missed that. Ugh!!! Is it running properly now?

It’s alright, I missed it too, I thought it just needed a good clean but when I looked into a bit more, it’s barometric readings were so off and then I took it to a shop where I know the mechanic who did it, and they ran a test on all of the sensors considering the air and fuel, and the MAF was bad just from that, they even took it out and cleaned it.

Well, I'm just glad it's running properly for you. Please feel free to come back in the future if you have questions.

Take care,
Joe

I definitely will, and thank you so much for helping me and going through everything with me, you’ve been a massive help, and I appreciate it.

You are very welcome. I don't want you to have more problems, but if you do, I hope to see you again in the future. Take good care of yourself.

Joe