P0171 Nightmare
 

So I feel like I've read everything there is on the subject over the internet. Long story short, gradually I've been getting an intermittent P0171 Check Engine Code with the VSC and traction lights. It would happen while the car would be idling at a stop light then later go away. I do experience weird idles sometimes, for example, sometimes if I have AC blasting at a stop sign my engine might dip to like 600-700 rpm before shooting back up to 1-1.2k. The car has never died on me. Furthermore, sometimes when I floor it I notice a little lag (1-2 seconds) before I feel like the engine really pull. I've replaced the upstream O2 sensor as well as the MAF sensor. Next course of action I believe I will replace the fuel injectors. I've checked for obvious air leaks but I see nothing. Any other ideas?

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Well, I managed to fix the code. I went ahead to change out the injectors and that seems to have been the issue. I've since put on another 150 miles after resetting the code and it hasn't come back. Usually the code would be coming back within ten miles. Hope this helps someone.

Keep us posted as to whether or not the codes come back as this might prove to be a fix for someone else farther down the road, so it's always nice when people take the time to list fixes they've found. :bow:

I know it's a different car but still a Toyota.
I've been battling this code on my sister's car for years.
So far in the last 4 years I've replaced all the vacuum lines, PCV valve, intake gasket, TB gasket, 02 sensors, injectors, fuel pump, engine temp sensor.
Still the same symptoms and code as yours persist.
She's gone to 2 mechanics and they couldn't find the problem.

At one point it got worse and I changed the air temp sensor on the airbox.
It ran much better but the original P0171 code and hesitation persists.

Well the code is back. I'm thinking it may have something to do with fuel delivery because after replacing the injectors I didn't seem to get any problems. I also replaced the intake manifold gasket for the heck of it as I heard these were common problems on our cars. Still the code comes back unfortunately. I have recently noticed a new issue however. In 1st and 2nd gear, after clearing any fault codes, the car will hesitate on acceleration and buck a little bit before it gets going. 3rd, 4th, and 5th gear no problems. When the CEL goes back on, this won't happen at these lower gears. The system is obviously comprnsating for the shortcomings correctly but I'm still confused as far as what it means.

Update: I've now replaced the fuel pump. I feel like this has solved the problem. There is no more hesitation at low rpm's so far. It's only been a week however. I will continue to update the thread.

0171 is a lean fuel mixture - yes, injectors will cause that, as will weak fuel pump, filthy intake valves, or even a clogged fuel filter. Change the filter. Then start with Techron, then move to the full BG Products treatment, then swap injectors (unless you find low pressure on the fuel rail, in which case pop in a new fuel pump)

When you pair that with a 0172 (rich fuel mixture) you've got a dead cylinder and need a motor. (1995 Toyota 4Runner, blew the motor twice. FPOS 3.0)

- Will England, Fine New Guy to the Forums
2005 Scion xB (Monday - son's car)

Other things that might cause a lean condition:

Bad fuel pump relay. Air intake leak. PCV system leak.

I've replaced injectors, fuel pump, fuel filter. I can't seem to find any air leaks in the intake or PCV. I am going to check the fuel pump relay tho. Code still comes back but only after driving a good amount (400 miles or so). Luckily, I can still pass smog after resetting it and driving 50 miles or so since the code doesn't come back immediately. I notice no symptoms other than sometimes when I floor it I lose some power right at the start. Makes me think air leak but I can't locate anything.

https://cimg1.ibsrv.net/gimg/www.sci...35f48f4b2a.jpg
This is all I can find on your problem.

Hope it Helps,

MR LUV

Wanted to update everyone. I believe the issue is fixed. I took out my new MAF sensor that I had already replaced and sprayed it with cleaner till it was soaking.
Reset the code and have driven 500 miles since and still no code. It seems to have been the MAF all along. Cold start accelerations still hesitate slightly but no other issues.

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@eatcrispycreme2 Im having this same problem and my mechanic can't seem to find anything. Have you gotten the P0171 code since your last post?

I have done the following:
Cleaned MAF
New PCV Valve
New Purge Solenoid
Smoke Tested and No leaks
Fuel Pressure Checked and fine
Injectors checked and fine
Changed Upstream 02 Sensor

Should I buy a new MAF?

Thanks

Good question. Here's a diy test video. Might save an unnecessary purchase.

Where be the video? :nails:

All I had to do was clean the original MAF sensor. After my 2nd time of doing it the issue was resolved and never returned. Spray it down very good and make sure it dries completely before installing and install as clean as possible.

Thank you! Ill clean it again :)

I slowly worked my way through the stupid P0171 issue (CEL, VSC light, etc) over the course of about a year. I did all these things below in the order listed:


1) PCV Valve - $5.67 at Rock Auto (but I think I got mine from Amazon…still, cheap)
2) MAF Sensor Cleaner - about $12 (I think) from Auto Zone. *Remove MAF Sensor; soak the crap out of it with Cleaner; use a small pipe cleaner/brush to knock off crud; soak the crap out of it again with Cleaner; LET IT DRY; re-install*
3) Replace Spark Plugs - Denso 5303 (Iridium) - $5.28 ea. at Rock Auto = $21.12

4) Replace Coil Packs (Ignition Coils) – Denso 6731306 - $54.79 at Rock Auto = $219.16

5) Replace O2 Sensor (fwd of the Cat “upstream”) – Denso 2344524 - $49.79 at Rock Auto



At every step, the car ran a little better but I would still get the P0171 Code. Weirdly, the interval that I received it improved as I went on. After I replaced the O2 Sensor, I received “P0171” once. I cleared it, then disconnected the battery for an hour or so (I’ve heard something along the lines of by doing that, something about the computer “relearns” the engine diagnostic…or some such. What-ehvs, I did it). I haven’t received “P0171” since and my car is running great! Now at 210k miles.



The only thing I’d recommend differently, is replace the O2 sensor before the Coil Packs just cuz it’s cheaper and maybe that was THE thing.