Dreaded P0171 lean Condition. - Toyota Nation Forum : Toyota Car and Truck Forums
Corolla 8th Generation (1998-2002) Specific discussion of the 8th generation

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post #1 of 12 Old 05-13-2019, 10:28 AM Thread Starter
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Dreaded P0171 lean Condition.

Hey guys so I have experienced a P0171 code for years. It comes and goes as it pleases. Over time I have replaced many part's and tried many possible fixes (Both o2 sensors, pcv valve, gas cap, cleaned the MAF sensor, fuel injector cleaner, etc. Also replaced the rusted out Fuel fill neck which kept the code away for a solid 5 months. My real reason for this post is because I have noticed Engine shaking/vibration at Idle. Now this only happens once the engine is warm. So if my engine is Misfiring once warm could it be related to the P0171 lean condition?Also important to note I never seem to get any Misfire code. I have never replaced Spark plugs either...
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post #2 of 12 Old 05-13-2019, 03:29 PM Thread Starter
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Another thing I should mention is Idle Surge after start up. Car also wants to die unless I let it idle for a minute before driving...
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post #3 of 12 Old 05-13-2019, 04:27 PM
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vacuum leak
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post #4 of 12 Old 05-13-2019, 09:31 PM
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Did u use aftermarket parts or genuine Toyota denso? Are your plugs the ones listed under your hood or just what the shop sold you?

Your vibes at idle is likely a mount that is bad. You need 2 people to check them but just do a break stand and watch for movement. Best done by a pro but the repair can be simple. Your car automatic?
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If any part of this was useful please click the thanks button to let me know it worked
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post #5 of 12 Old 05-13-2019, 10:54 PM
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get a code reader and report the engine parameters at the time lean code was set

This is called freeze frame data
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post #6 of 12 Old 05-13-2019, 11:24 PM
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Quote:
Originally Posted by DannoXYZ View Post
vacuum leak
^ this..

- check for vac leaks
- take a garden hose and douse the intake manifold/air intake area while engine is idling
- listen for idle changes to locate your leak
- use carb cleaner or whatever if you're uncomfortable with water..






1995 2.2L Camry 5sfe engine
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post #7 of 12 Old 05-14-2019, 03:37 AM
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The surging idle is primary clue. ECU is trying to adjust IAC to compensate for leak, but results in a roller-coaster ride of catch-up and missing back & forth.

Youíre right about other clue, it gets shaky and can even stall when warmed up due to lean mixtures. Extra air is getting sucked in along intake-tract somewhere after MAF, thus is not measured by MAF. Therefore, ECU doesnít inject extra fuel to match whatís sucked in by vacuum leak leading to lean mixtures. Itís better when cold because ECU properly detects cold-start and engages cold-start cycle with extra fuel (+6 to 25% more depending upon actual ambient temp).

There is absolutely nothing that you can do with scanner that will find vacuum leak (other than confirming leak exists by low MAF readings and positive fuel-trims; donít kill the messenger, itís working fine). Absolutely zero parts you can replace that will fix this. Have to do good ol' fashion troubleshooting like smart mechanics have been doing for 100-years.
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post #8 of 12 Old 05-14-2019, 10:31 AM
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What Year is the vehicle?

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post #9 of 12 Old 05-14-2019, 05:01 PM
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All this reliance on electronics makes people soft and not capable of critcal thinking and logic. They just want answers and be told what to do. When apocalypse comes, those who can't set traps for rabbit or kill with your bare hands are gonna starve to death! Zombies are gonna getcha even though they're slower than molasses! Come see our newest game in Orlando: http://nomadicvr.com

Now, i'm going to show you some survival skillz. Put down the xbox, or tablet or whatever gizmo is your temple of Truth and get hands-on dirty and touch your car physically and mechanically. Touch it, feel it vibrate, learn how it sounds when it's healthy and when it's sick. Pull and yank on hoses to see if idle note changes. Squirting with propane, carb-cleaner, water or even strategic aiming of pee can help, but you need to have some prior experience to recognize the subtle change in idle tone. And you need to know where to squirt.

Here's a sure-fire 100% way to find vacuum leaks with positive visual confirmation.

1. Plug your exhaust with banana, potatoe, cork, wet-rag or whatever gives 100% blockage

2. Make a plug fitting that replaces MAF on intake hose with compressor quick-fitting


3. Install your plug into intake hose which normally connects to outlet of MAF


4. Then set compressor to 3-5psi and connect to fitting

5. Squirt soapy water at every connection point from intake hose all the way to intake valves. Every seam, every joint, every clamp, etc. Pay particular attention to intake-manifold to head mating surface. Also injector tips.

In this case ironically, I had leak at external idle-valve. There's O-rings and seal inside case of idle-valve that needs replacing.


And another leak at throttle-body/TPS. There's O-rings on both sides of butterfly shaft that needs refreshing.


Also leak by dipstick tube. Looks like someone previously replaced O-ring with one that's too big. New correct O-ring with some sealant takes care of that!


Bubbles stay around leaks and gives you time to find them. Squirting propane isn't nearly as effective because you need to squirt at ALL leaks simultaneously for enough to get into engine to affect idle note. And you can't see propane and see exactly where it was sucked in. Bubbles are easier!!!
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post #10 of 12 Old 05-16-2019, 01:19 PM Thread Starter
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Quote:
Originally Posted by DannoXYZ View Post
The surging idle is primary clue. ECU is trying to adjust IAC to compensate for leak, but results in a roller-coaster ride of catch-up and missing back & forth.

Youíre right about other clue, it gets shaky and can even stall when warmed up due to lean mixtures. Extra air is getting sucked in along intake-tract somewhere after MAF, thus is not measured by MAF. Therefore, ECU doesnít inject extra fuel to match whatís sucked in by vacuum leak leading to lean mixtures. Itís better when cold because ECU properly detects cold-start and engages cold-start cycle with extra fuel (+6 to 25% more depending upon actual ambient temp).

There is absolutely nothing that you can do with scanner that will find vacuum leak (other than confirming leak exists by low MAF readings and positive fuel-trims; donít kill the messenger, itís working fine). Absolutely zero parts you can replace that will fix this. Have to do good ol' fashion troubleshooting like smart mechanics have been doing for 100-years.



Wow that makes perfect sense. Thank you so much the the reply and your time. I think I might try the Carb cleaner trick. Which areas I should check/spray for leaks? It's hard to tell what I'm looking at Vacuum line wise....I remember reading that Intake manifold gaskets going bad are common on our Cars?

Last edited by Evan93; 05-16-2019 at 03:09 PM.
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post #11 of 12 Old 05-16-2019, 01:20 PM Thread Starter
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Quote:
Originally Posted by funman1 View Post
What Year is the vehicle?
2000 Corolla
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post #12 of 12 Old 05-16-2019, 04:44 PM
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Quote:
Originally Posted by Evan93 View Post
Wow that makes perfect sense. Thank you so much the the reply and your time. I think I might try the Carb cleaner trick. Which areas I should check/spray for leaks? It's hard to tell what I'm looking at Vacuum line wise....I remember reading that Intake manifold gaskets going bad are common on our Cars?
Quote:
Originally Posted by DannoXYZ View Post
Every seam, every joint, every clamp, etc. Pay particular attention to intake-manifold to head mating surface. Also injector tips.
You're most welcome. Yup, squirt everywhere intake-air flows. From MAF all way to intake-valves. Every joint where hoses has an end with clamp should be squirted 360-degrees all way around. Squirt along body of every hose. Each intake-runner may have leak, so squirt all 360-degrees around every runner where it touches head.

Bubbles would be easier and take less time! Good luck!
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