p0171 persists - LotusTalk - The Lotus Cars Community
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post #1 of 20 (permalink) Old 11-15-2016, 06:53 PM Thread Starter
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p0171 persists

Last month, after having the front clam and L rocker panel replaced on my 2005 Fed Elise, my Engine light threw a p0171 on my OBD-II. Only other thing noticed is an occasional 'stutter' at idle; it doesn't die, but seems close.

After removing/spray-cleaning the MAF sensor (yes, down the 'hole'), it still throws the code. I don't see any spots for obvious leaks, but I did see the recent thread by @rkalina where many of you suggested ways to test for them. I may try using the left-over spray to do that tomorrow.... but I'm tempted to go ahead and order a cheap MAF replacement in the hopes that might do the trick.
(FWIW, my car has the ForceFed mod. since 'birth', no issues in previous 10 years of ownership...)

Any other suggestions?

--Doug Stratton--

'05 Elise in Saffron Yellow ,Sport pack, ForceFed Intake, Stage II Exhaust, Potenza RE71R, LidBone, Stebel Nautilus AirHorn
First mid-engine drive: '74 Porsche 914 2.0 in Solar Yellow (Dad's car)
BEST mid-engine drive: '05 Lotus Elise in Saffron YELLOW!!!
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post #2 of 20 (permalink) Old 11-15-2016, 06:57 PM Thread Starter
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I also saw the suggestion of the more advanced diagnostics information that can be obtained using a better OBD dongle with the appropriate app... sounds kinda groovy, but I might just opt for a pro mechanic before going that route...

--Doug Stratton--

'05 Elise in Saffron Yellow ,Sport pack, ForceFed Intake, Stage II Exhaust, Potenza RE71R, LidBone, Stebel Nautilus AirHorn
First mid-engine drive: '74 Porsche 914 2.0 in Solar Yellow (Dad's car)
BEST mid-engine drive: '05 Lotus Elise in Saffron YELLOW!!!
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post #3 of 20 (permalink) Old 11-16-2016, 11:33 AM
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This is a bit of a gremlin with these cars. Any number of things can happen. MAF, vacuum leak, 02 sensors, fuel injector seal, coil packs...

There are several threads about this.

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post #4 of 20 (permalink) Old 11-16-2016, 12:58 PM
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I hate the idea of throwing parts at a problem to find the solution when there are valid, free tests you could be doing instead. If it has the problem right away, then it is not the O2 sensor (they are only used once they warm up). If you are not seeing problems anywhere but at idle, then I'd focus on things that are different between idling and under load. For instance, your MAF is always used, so that is not a likely candidate unless it is a problem related specifically to how it acts with very low airflow. So it is definitely possible, but I'd say there are more likely candidates first. Your IAC valve is one major candidate for idle problems, but it won't make it go lean without raising idle. From this line of reasoning (which makes some assumptions), I'd focus on a leak, bad spark, or dirty injector. Anything that can cause a misfire at low rpm could be misconstrued as a lean condition and would cause a stumble.
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post #5 of 20 (permalink) Old 11-16-2016, 01:23 PM Thread Starter
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There's not really an idle problem as far as I can tell, I just mentioned that rare idle 'stumble' as the only 'symptom' that I could think of. I'm not even sure if it wasn't already there before the engine light started coming on (always p0171).

I'm not sure what my next step should be. I was hoping there might be an easy find/fix in my situation, but perhaps there really isn't, and that's OK. I can always try to find a mechanic. Just not sure who in Atlanta to take it to, so perhaps a separate thread...

--Doug Stratton--

'05 Elise in Saffron Yellow ,Sport pack, ForceFed Intake, Stage II Exhaust, Potenza RE71R, LidBone, Stebel Nautilus AirHorn
First mid-engine drive: '74 Porsche 914 2.0 in Solar Yellow (Dad's car)
BEST mid-engine drive: '05 Lotus Elise in Saffron YELLOW!!!
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post #6 of 20 (permalink) Old 11-16-2016, 01:30 PM
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Quote:
Originally Posted by AtlantaLotusLove View Post
There's not really an idle problem as far as I can tell, I just mentioned that rare idle 'stumble' as the only 'symptom' that I could think of. I'm not even sure if it wasn't already there before the engine light started coming on (always p0171).

I'm not sure what my next step should be. I was hoping there might be an easy find/fix in my situation, but perhaps there really isn't, and that's OK. I can always try to find a mechanic. Just not sure who in Atlanta to take it to, so perhaps a separate thread...
If the CEL comes back on after clearing it and the idle problem is not seen in that same time period, then it is just a distraction. If so, you really, really, really need to take it to a mechanic familiar with the tune on it.
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post #7 of 20 (permalink) Old 11-16-2016, 03:04 PM
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Quote:
Originally Posted by AtlantaLotusLove View Post
I also saw the suggestion of the more advanced diagnostics information that can be obtained using a better OBD dongle with the appropriate app... sounds kinda groovy, but I might just opt for a pro mechanic before going that route...
Is your hesitance due to dollars or lack of expertise? If the former, note that the bluetooth OBD dongles are quite reasonably priced (something like $10-20). If it is the latter, please allow me to share my tin foil hat with you...

I too had the P0171 and could not pin down the root cause. I tried many of the strategies listed above, and with the aid of appropriate OBD data, and decided that the sensors were not faulty. I could not find evidence of an air leak or of the engine control strategy trying to compensate for a lean condition, in spite of the error code. I kept trying different things, clearing the code each time, only to have it come back. Although it is very tempting to just throw money at the problem (i.e. buy new sensors in spite of the lack of evidence that they are faulty), I chose to keep looking for data that there was actually a problem and thereby pinpointing the source. I still have not found any; I recommend a tin foil hat because I lack confidence that a mechanic would serve your best interest in this case- it is far too easy to recommend spending money on parts based on preconceived notions of what causes a lean error code.

Ultimately I just kept data logging, trying to replicate the conditions which tripped the error code while I took data logs. In spite of the recurring error code, I took a long road trip to the D.C. area from MI. By the end of the trip, the code no longer came on (this has been since mid September). Could it have been a long, hot drive affecting the sensors? Could the battery voltage have recovered during the long drive? Maybe the change in gas stations along the way? I don't know what it was, but the end result is consistent with my data which indicated that there was not really a problem.

If you end up taking the car to a mechanic please ask them to show you the data or evidence which motivates their recommendation. If they tell you 'this is what typically causes lean conditions', I suspect that they also did not find strong evidence.
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post #8 of 20 (permalink) Old 11-16-2016, 05:43 PM Thread Starter
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@Obeisance Thank you so much for that!

It's not dollars, it's a lack of confidence and expertise to figure it out, or even know what to do with the information/data collected. I'm also due to have my annual inspection (which, undoubtedly, it will not pass), so I feel pressured for time to avoid the penalties to be incurred... I've asked the local Lotus chapter members for a referral to a decent mechanic to no avail. There's the local dealer, that also sells all sorts of other exotics, but they're probably apt to just start replacing things as you said. Perhaps I ought to at least talk to them and see if they seem to have any expertise in this area...

In the meantime: how do I find this bluetooth dongle? ... apologies if it's been asked many times before!

--Doug Stratton--

'05 Elise in Saffron Yellow ,Sport pack, ForceFed Intake, Stage II Exhaust, Potenza RE71R, LidBone, Stebel Nautilus AirHorn
First mid-engine drive: '74 Porsche 914 2.0 in Solar Yellow (Dad's car)
BEST mid-engine drive: '05 Lotus Elise in Saffron YELLOW!!!
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post #9 of 20 (permalink) Old 11-17-2016, 05:07 AM
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Amazon has tons of them, but basically you want one with the ELM chip. Only go with bluetooth if you have an Android device (phone or tablet). iPhones don't work with the Bluetooth ones, so you'll need a wifi-based one if you want to use an iPhone with it. Then you'll need an app; I use Torque Pro for my android tablet and DashCommand for my iPhone.

Added: The CEL comes on when your short-term fuel trim goes past a threshold (around 17% I think), so that's the variable you want to watch and see when it is pegged out.
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post #10 of 20 (permalink) Old 11-17-2016, 05:14 AM Thread Starter
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Quote:
Originally Posted by cyow5 View Post
Amazon has tons of them, but basically you want one with the ELM chip. Only go with bluetooth if you have an Android device (phone or tablet). iPhones don't work with the Bluetooth ones, so you'll need a wifi-based one if you want to use an iPhone with it. Then you'll need an app; I use Torque Pro for my android tablet and DashCommand for my iPhone.

Added: The CEL comes on when your short-term fuel trim goes past a threshold (around 17% I think), so that's the variable you want to watch and see when it is pegged out.
Thanks. I'm an iPhone user. I'll check these out once the domestic front settles down... daughter got rear-ended by a cement truck yesterday.. mri, ct, neurosurg...

--Doug Stratton--

'05 Elise in Saffron Yellow ,Sport pack, ForceFed Intake, Stage II Exhaust, Potenza RE71R, LidBone, Stebel Nautilus AirHorn
First mid-engine drive: '74 Porsche 914 2.0 in Solar Yellow (Dad's car)
BEST mid-engine drive: '05 Lotus Elise in Saffron YELLOW!!!
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post #11 of 20 (permalink) Old 11-17-2016, 05:20 AM
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Originally Posted by AtlantaLotusLove View Post
Thanks. I'm an iPhone user. I'll check these out once the domestic front settles down... daughter got rear-ended by a cement truck yesterday.. mri, ct, neurosurg...
Yeah, I'd say that takes priority! Best of luck with everything
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post #12 of 20 (permalink) Old 11-17-2016, 05:58 AM Thread Starter
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I'll check back in when I get some more info... thanks for all the help!

--Doug Stratton--

'05 Elise in Saffron Yellow ,Sport pack, ForceFed Intake, Stage II Exhaust, Potenza RE71R, LidBone, Stebel Nautilus AirHorn
First mid-engine drive: '74 Porsche 914 2.0 in Solar Yellow (Dad's car)
BEST mid-engine drive: '05 Lotus Elise in Saffron YELLOW!!!
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post #13 of 20 (permalink) Old 11-17-2016, 06:40 AM
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Wow. We all hope your daughter will be fine. Good luck.
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post #14 of 20 (permalink) Old 11-17-2016, 08:11 AM
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I doubt it's a bad MAF sensor. I'd check for leaks.
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post #15 of 20 (permalink) Old 11-17-2016, 08:17 AM
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I use a small propane tank, with a hose attached to it. This allows pinpointing the (a) leak vs. spraying an aerosol around the area.
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post #16 of 20 (permalink) Old 11-17-2016, 03:18 PM
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I've been trying to chase this down on one of my Elises. I'm fortunate to have two which means I can simply swap some parts. My symptoms are probably different from yours:
- When cold, will idle perfectly.
- After dropping to low idle (warm), the idle will start to roll
I believe that the car has an intake-side air leak. It sounds like the ECU tries to slow the idle down, and as it does, I hear a sucking/whistle sound that increases in amplitude as the idle speed decreases until the car wheezes a bit and then the rpms jump up high to prevent a stall. This process seems to result in what sounds like a rolling idle with a cycle time of about 30 seconds. The car doesn't stall.

What I have done:
- Freed the definitely stuck IAC (I verified operation using a PWM source before cleaning)
- This appears to have stopped the idle from going so low that the car stalled
- Smoke-tested the intake with a DIY paint can smoke tester (no apparent leaks)
- Used brake clean to spray down the intake to detect idle speed changes (no apparent leaks)
- Cleaned the MAF sensor (no change)
- Swapped the MAF sensor with the other car (no change)
- Swapped the processor with the other car (which has no CELs)
- Initially the car ran poorly, but after a few minutes of idling, the car ran the same (rolling idle) and threw the P0171
- Incidentally, I apparently swapped the processors quickly enough that the SMOG readiness monitors were left in a ready state
- Removed the exhaust at the collector gasket to check for an exhaust-side leak
- Removed the intake manifold and replaced the intake and injector seals (~$20, no change)

I usually use a length of rubber hose to find the source of air leaks. I haven't been able to really figure out where I hear the leak best. It seemed like between cyl 2 and 3 at the intake runners.

Last edited by Roundabout; 11-25-2016 at 07:39 PM.
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post #17 of 20 (permalink) Old 11-17-2016, 03:29 PM
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I had same issues, still trying to resolve, though I have a intercooled supercharger which adds more pain points. Trackspec has it now....and they are finding all kinds of my shoddy work lol. Anway, for your case, can a brake booster leak do the same? meaning the vacuum hose that runs to the booster...it could do this and the line is all the way to the front--since you have done everything else possible as far as i can tell.

Quote:
Originally Posted by Roundabout View Post
I've been trying to chase this down on one of my Elises. I'm fortunate to have two which means I can simply swap some parts. My symptoms are probably different from yours:
- When cold, will idle perfectly.
- After dropping to low idle (warm), the idle will start to roll
I believe that the car has an intake-side air leak. It sounds like the ECU tries to slow the idle down, and as it does, I hear a sucking/whistle sound that increases in amplitude as the idle speed decreases until the car wheezes a bit and then the rpms jump up high to prevent a stall. This process seems to result in what sounds like a rolling idle with a cycle time of about 30 seconds. The car doesn't stall.

What I have done:
- Freed the definitely stuck IAC (I verified operation using a PWM source before cleaning)
- This appears to have stopped the idle from going so low that the car stalled
- Smoke-tested the intake with a DIY paint can smoke tester (no apparent leaks)
- Used brake clean to spray down the intake to detect idle speed changes (no apparent leaks)
- Cleaned the MAF sensor (no change)
- Swapped the MAF sensor with the other car (no change)
- Swapped the processor with the other car (which has no CELs)
- Initially the car ran poorly, but after a few minutes of idling, the car ran the same (rolling idle) and threw the P0171
- Incidentaly, I aparently swapped the processors quickly enough that the SMOG readiness monitors were left in a ready state
- Removed the exhaust at the collector gasket to check for an exhaust-side leak
- Removed the intake manifold and replaced the intake and injector seals (~$20, no change)

I usually use a length of rubber hose to find the source of air leaks. I haven't been able to really figure out where I hear the leak best. It seemed like between cyl 2 and 3 at the intake runners.
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post #18 of 20 (permalink) Old 11-17-2016, 03:42 PM
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I had same issues, still trying to resolve, though I have a intercooled supercharger which adds more pain points. Trackspec has it now....and they are finding all kinds of my shoddy work lol. Anway, for your case, can a brake booster leak do the same? meaning the vacuum hose that runs to the booster...it could do this and the line is all the way to the front--since you have done everything else possible as far as i can tell.
Yes, it could. I'll check that out. Maybe I can disconnect both ends, put a plug in one end and try to draw a vacuum with the mighty-vac.

It appears to me that there really are a lot of hoses underneath the intake manifold, but only the crankcase ventilation hose appears to be a possible leak point. The rest look to carry coolant or oil.

Another thing I was thinking of trying was to plug or stub all of the lines and see if that makes a difference.

I read that the CANP (Canister Purge Valve) can get stuck open and result in an air leak. I think the technique above will be what I try first -- simply capping the lines one by one since the problem is so repeatable.

Last edited by Roundabout; 11-18-2016 at 11:31 AM.
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post #19 of 20 (permalink) Old 11-22-2016, 10:49 AM
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couple of things.
Check your maf sensor o ring. Make sure its seated properly.
I was checking a hesitation issue when I went supercharged it wasn't there NA. I have a brand new tacoma with 100 miles on it ( I say the miles to indicate a new maf), which uses the same maf sensor and i swapped it. my STFT were better with the MAF from the tacoma. Although my MAF wasn't bad, it wasn't as accurate over time, even after cleaning it with the MAF cleaner spray. I ordered a new OEM one off ebay and it runs better.

part number is 2220422010

Heres a link to it new:
New OEM 2220422010 Prius Yaris 1.5L Mass Air Flow Meter 22204-22010 For TOYOTAUS | eBay

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post #20 of 20 (permalink) Old 11-25-2016, 04:14 PM
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Hallelujah the idle is perfect. It idles in a range of about 50 rpms now and the emissions status monitor for the catalyst is set. It was because a previous owner along the way (or mechanic) swapped the O2 sensor harness connectors. Purple wire goes to the post-cat. This is probably no help for the OP, however, as I wouldn't think that this is a common problem. I guess this confirms that warm idle is controlled, in part, by O2 sensor response. The car idled fine when cold, but rolled when warm.
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