I'm just posting to see if anyone else has had a similar experience as me. I have a lean code p0171 that shows up right on startup, but intermittently, not every startup. I clear the codes each time so I can see when it comes in and it still seems random. I also have an occasional (random) misfire at high rpm/heavy acceleration like a hard extended pull. I want to say they are related probably. All my dynamic intake vacuum lines(all 3, along with my air intake manifold). Any input is much appreciated, I recognize it might be a vacuum leak however it's so inconsistent that I think it might not be. My current suspicions are a bad injector, bad fuel pump, funky vacuum leak, or a bad upstream O2 sensor. I also have extra sensitive/jerky throttle response at low rpm(I've compared across rx8s, this one is extra sensitive). Thanks again.

 

What are the fuel trims while warmed up and idling? That should be a clue.

 

I can look when I'm home this weekend, what should I be looking for in them specifically to indicate specific issues?

 

Long-term and short-term fuel should be near 0 on a healthy car, and MAF rate should be about 5.7g/sec on an 800rpm idle. If they're high (max is +25) and MAF rate is low, you're getting in unmetered air somewhere - vacuum leak. If they're low, which would be unusual, you might have reversed ignition or fuel injector connectors. If they bounce around wildly we could look at fuel injectors or fuel pressure problems. But 95% of the time issues like this are vacuum leaks.

 

Awesome thank you very much!

 

My mass air flow is around 4.55 g/s at 950rpm, and my long-term trim is 22.7 percent with my short term steadying around 3.1 percent but it was 14.1 for a minute. From what you mentioned it seems like I have a vacuum leak then?

 

Yep sizeable vacuum leak. Is the intake stock? Look for cracked vacuum likes, broken elbows, etc. Some sre under the throttle body and under the upper manidolf.

 

Yep I figured it out. My vacuum solenoid supply line was disconnected for some reason. Thanks for the advice again.

 

Glad you were able to locate the problem. I had the same code and it ended up being the o2 sensor that goes to the exhaust manifold (sensor 1/ bank 1). After driving the car on my commute - it would die out on the exit when i put the car in neutral. It would also spike from almost dying at the low rpm's and go to 3k trying to stay on. My gas mileage was also affected by losing about 2mpg a gallon on average. Just wanted to post this as another possible trouble-shooting solution for anyone else coming across this CEL code.

 

Glad you were able to locate the vacuum leak. You'd be surprised at what one small vacuum leak can do to your fuel trims and how much it can effect how the engine runs.