P0171 CEL Thread - Everything you ever wanted to know?

[Wagon Of Fury]

I think I just fixed this problem after living with it for about two months. If I did, I will hang my head in shame for the simplicity of it.

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[Scubydood]

I recently started getting this code too. Subaru thought it was either the maf or afr sensor. Had tuner check it out and code still came back when they tested with new parts. They said my DW850's are going bad? I bought them new only two tears ago.

[Wagon Of Fury]

Check the simple stuff, like vacuum leaks. Your injectors ? Unlikely, but send them off to RC for cleaning if it eases your mind.

[kurtwz]

Would running the car w/o the restrictor pill in place cause this code? Also, if i would fix the problem and drive the car w/o clearing the code on a scanner, how long would the car take to clear the code itself?

[kurtwz]

Still need to know how long you'd have to drive the car with the problem fixed for the check engine light to turn off. Thanks

[Wagon Of Fury]

Originally Posted by kurtwz

Would running the car w/o the restrictor pill in place cause this code? Also, if i would fix the problem and drive the car w/o clearing the code on a scanner, how long would the car take to clear the code itself?

Anything that messes with the air intake flow could cause this. Anything.

Originally Posted by kurtwz

Still need to know how long you'd have to drive the car with the problem fixed for the check engine light to turn off. Thanks

Depends on the type of CEL.
Buy a $45 scantool or go to VatoZone and let them clear it for you.
Or google OBD readiness

[kurtwz]

I’m wrestling with this problem. I have an 02 WRX w/ 101K mi. It used to be a stage 3 car (16G turbo, pink injectors, Walbro fuel pump), but I’ve reverted it back to stock. The car was not driven for a couple years before I just recently started driving it again and having problems with it. The car is now completely stock in terms of the powertrain. The installation of the injectors and stock fuel pump went well. Car is running great. Smooth strong power, smooth stable idle, no sputtering, etc.. The only complaint would be that the throttle response seems a little slow. About 150 miles ago I got the P0171 code and haven’t been able to fix it yet. Here’s what I’ve done:

1. Checked vacuum lines: checked all vacuum lines around turbo, IC, air intake. Everything seems good and tight.
2. Checked air box: tight.
3. MAF: cleaned thoroughly using MAF sensor cleaner.
4. PCV Valve: cleaned thoroughly using MAF sensor cleaner. I know it’s best to replace this since it’s only a couple bucks, but I didn’t have one on hand and the stores were closed, so I had to clean it. I DID notice that there was a fairly substantial amount of oil (I think it was oil) in the tubes that go from the PCV valve to the black plastic nozzle and in the tube from the black plastic nozzle to some other nozzle (on the air intake I think). That’s bad, right? Could that cause the P0171 code? There was so much oil that I think it got into the IC y-pipe. That possible?

I haven’t cleaned/replaced the MAF, O2 sensor, IACV, or MAP sensor. I want to try cheaper potential fixes before I start replacing parts. The IACV gasket is on order, so I plan on going that, tho.

Can anyone offer advice specific to my situation? Specifically I’d be interested to know whether you think the PCV valve being that messed up could cause the code. Also, I’d love to know how long after the root cause is fixed I can expect the light to turn itself off. THANKS!!!

[kurtwz]

Originally Posted by Wagon Of Fury

Anything that messes with the air intake flow could cause this. Anything.

Restrictor pill on order.

Depends on the type of CEL.
Buy a $45 scantool or go to VatoZone and let them clear it for you.
Or google OBD readiness

I have a scanner. It's P0171 error code.

[J. Steinbeck]

I got this code a couple of weeks ago after doing some work on my car. Car idled like ****.

Since I removed the intercooler, I assumed I must have created a post turbo intake leak of some kind. I reinstalled and removed the intercooler three times and looked EVERYWHERE under it trying to find what in the world I messed up.

Then... low and behold, while I was at work something occurred to me. I went back to the car, popped the hood, and there, directly in front of me, was the purge control solenoid on the front of the intake, pushed off slightly from its straw sized hose.

DOH! Turns out I was resting my palm in that area while I was working and knocked it loose. Put it back on, zip tied it tight (in other words, I turned the tie into a small hose clamp), and everything was back to normal.

The point in the story is to make sure you check around that thing, as it's easy to knock the little lines that go into and out of that round black piece loose, and they can definitely create a vacuum leak significant enough to cause this code.

Perhaps this has already been stated, but I was honestly too lazy to search back through the 500+ pages of this thread.

[kurtwz]

Originally Posted by J. Steinbeck

Perhaps this has already been stated, but I was honestly too lazy to search back through the 500+ pages of this thread.

Thanks for the tips, Steinbeck. My car is idling and running all around great. Also, I've spent several hour under the hood at this point trying to fix this and don't think I'll find a loose hose at this point.

***UPDATE***
I just drove my car over lunch to get new tires. After I picked it up I noticed the check engine light was OFF. I went back and asked them whether they disconnected the battery/reset the ECU (just to be sure) and they said they did not. Then on the way back to work the light came back on after only 5 miles of driving. So I think I'm starting to have an impact, but it's not totally solved.

Anyone else have a situation where the light turns off, then comes back on very shortly thereafter? BTW, I scanned it just to make sure and it shows one fault of P0171 and one pending fault of P0171, so it’s the same as the original code.

[WickedTSI]

Had this code for about 2 weeks. It turned out to be a bad Maf, car runs great now.

[Sindvs]

i recently bought a 2007 sti and it has a aps cold air intake the previous owner installed and i drove it for a couple days and i got a cel i got the infamous p0171. i am not sure if its the CAI but i looked at the aps website and it says tuning maybe required, so i was thinking of buying a cobb access port do a data log and have some one make me a map do you think this will work?

[Wagon Of Fury]

Originally Posted by Sindvs

i recently bought a 2007 sti and it has a aps cold air intake the previous owner installed and i drove it for a couple days and i got a cel i got the infamous p0171. i am not sure if its the CAI but i looked at the aps website and it says tuning maybe required, so i was thinking of buying a cobb access port do a data log and have some one make me a map do you think this will work?

If you have a boost leak somewhere, you will get this. So re-read the thread and find your leak. Or, spend hundreds of dollars on a AP and a tune, and then still have a leak, which will have to be found, before you get a (re) retune.

[Timmy_M2000]

Originally Posted by Wagon Of Fury

If you have a boost leak somewhere, you will get this. So re-read the thread and find your leak. Or, spend hundreds of dollars on a AP and a tune, and then still have a leak, which will have to be found, before you get a (re) retune.

True. I FINALLY sourced mine to pinholes on the weld in my header right in front of my AFR, in conjunction with a couple other small leaks. Boost checks are a solid way to find them. Many different apparatus' can be used to find them. I used one from dnorton here on the forums. Worked great, found all my topside leaks at least.

[SimonTuffGuy]

Originally Posted by kurtwz

Anyone else have a situation where the light turns off, then comes back on very shortly thereafter? BTW, I scanned it just to make sure and it shows one fault of P0171 and one pending fault of P0171, so it’s the same as the original code.

Mine went off twice during the time that I had the CEL, but it only seemed to go off when I drove in heavy rain. After it dried up, the CEL returned.

I finally found the culprit of mine... I've got a stock 02 WRX with 135k on it. I replaced the fuel filter and ran a good bottle of cleaner through it. Visually checked all the lines that I could see for cracks or being disconnected, listened, nothing. (I did have a leak from when I installed my OEM boost gauge. It was on the inside where the kit I bought connected to the stock hose, and I resolved that with a heavy duty twist clamp.) I cleaned the air filter, which was pretty crusty and sprayed the MAF with the special cleaner. That was also coated with the same crud that was on the filter. So - CEL came back after those cheapy fixes, so I opted for the O2 sensor next, since it was the next cheapest option. $119 off Amazon and an hour install, the CEL returned this weekend after my 100 mile mark and the car continued to "hesitate"... It seemed like under full boost in any of the gears, but I saw it mostly in 3rd-5th when going up a hill... It just "chugged" almost.

Had a friend pick up an 02 WRX earlier this week, so I went to meet up with him on Sunday. We swapped MAFs for the day and I took the car out to camp and for a 120~ mile trip. Instantly, the car responded better, no chugging, no hesitation... Realistically, I went 120~ miles and should've gone further, but the wife wasn't happy after the 300 mile trip from Saturday and had enough on Sunday. Anyways - I ordered up the Denso MAF last night from Advance, since they were running a 20% off sale and it should be here sometime this week. All in time to get my inspection done, without having to reset the code, hit 80 miles and hope that the light didn't come back on before they got it on the computer.

Thanks for the help and suggestion of this thread... And good luck to anyone battling this damn code.

[czum09]

So my car has had this CEL for about a month... heres my symptoms, bad throttle response, idle feels like its on three cylinders, and sometimes the rpms dip to like 200 rpm. Any ideas?

[ceasar]

Originally Posted by czum09

So my car has had this CEL for about a month... heres my symptoms, bad throttle response, idle feels like its on three cylinders, and sometimes the rpms dip to like 200 rpm. Any ideas?

Clean ur maf sensor. if it doesnt help use ur friend's maf for like 10 min, so u r able to tell if ur maf is shot or not. Post results.

[czum09]

I cleaned it and the CEL still came back after 15 miles of city driving. I will see if I can use my buddies. Also sometimes the car over boosts... It's so weird.

[Illest_WRX209]

I practically checked every instruction on this thread and I still cant seem to find the problem. The previous owner of my car had not driven the car for over a year and when I got it I read the codes it said bank 1 too lean and cylinder 1 and 3 misfire . I've replaced the front o2 sensor spark plugs fuel filter checked all vacuum lines grounds they all came out good. Maf is cleaned checked to see if the intake were mounted on correct. Any ideas that the injectors or coil plugs could be the culprit . After all the car has been sitting for a year. And also I may add it runs perfectly fine but when it's below a quarter tank it tends to jerk like as if there's a fuel cut somewhere. Any suggestions would be highly appreciated . Thanks , Johnny

[devlmaycry]

Had several codes after the TGV delete, even though I left my motors and rods in, including this one. Fixed all of the other codes related to the TGV being sticky except the P0171 until I read this thread. Tracked it down in about 5 minutes. The FPR hose had gotten knocked off or not hooked back up. Fixed it and the code hasn't come back. Great thread!

[st267]

Thanks so much for this write up. Finished a clutch job Sunday started the car up and it ran like hell. ROUGH.. barely idling, staled once. Finally threw the P 0171 code after about 5 miles of driving. Took 10 mins Monday night to quickly check the air box and hoses in sight. Low and behold, on that little blue T connector between the bottom front of the IC and the intake manifold, had one of the vacuum lines off. Reconnected it and the rest is history

[txl146]

Here is how I fixed my P0171 CEL (repost).

[mmiller2002]

WOW, that's a lot of $$! At what step was the MAF replaced the first time?

[txl146]

MAF was replaced with another one probably a year before car started to have CEL problem. Never thought it was bad MAF since it looked almost new.

[Gethin]

re clocking my IACV actuator fixed mine. I tried a new front o2, MAF sensor, smoke leak test (nothing found) , IACV gasket, cleaning IACV by removing the actuator, cleaning with qtips etc, checking all hoses etc etc etc but it always came back. I think it initially was caused by a bad front o2 which I replaced. Symptoms included a lumpy idle, especially when cold.

I ended up loosening the IACV actuator bolts, clocking it until the gap between the spinning edge and the housing was as small as possible, then tightening the actuator bolts (make sure the tab that protrudes out of the spindle fits into the cap correctly if you take the actuator off) and bolting it all back up. I must have put it back incorrectly last time when trouble shooting the whole affair.

Idle is now rock solid, and no more CEL.