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Have you determined if the MAF sensor isn't out of whack? If it's telling the car less air is entering than actually is, it will show up as lean because it will need to add a bunch more fuel to compensate for all the extra air it doesn't see from the MAF. Your spark tables will be affected as well due to the load being computed lower than reality.
 

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Discussion Starter #22
See post #9 above.

There are 8 pieces of hose in that line.
That’s the web page I used to locate all the hoses. Replaced them all with new hoses. Great article!

Have you determined if the MAF sensor isn't out of whack? If it's telling the car less air is entering than actually is, it will show up as lean because it will need to add a bunch more fuel to compensate for all the extra air it doesn't see from the MAF. Your spark tables will be affected as well due to the load being computed lower than reality.
I had read that if you unplug it while the car is running, and the car starts running worse the sensor is fine, and that if the car runs better it’s bad. I unplugged it, and the car ran noticeably worse.

I’m new to these things though, and maybe this isn’t the case for the T-Birds
 

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Well, the car will idle rough with the MAF unplugged because it runs off some basic tables to calculate fuel delivery (more or less based on RPM and TP). It also tends to run a bit rich with the MAF unplugged. Acceleration and cruise would improve if the MAF is having issues.

Example of someone who had to replace the MAF to get rid of his lean code: Engine code: "System too lean"
 

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Discussion Starter #24
Well, the car will idle rough with the MAF unplugged because it runs off some basic tables to calculate fuel delivery (more or less based on RPM and TP). It also tends to run a bit rich with the MAF unplugged. Acceleration and cruise would improve if the MAF is having issues.
I’m gonna go unplug it and see if the car accelerates better. I only have unplugged it while in Park. Haven’t tried to actually drive it like that

Well, the car will idle rough with the MAF unplugged because it runs off some basic tables to calculate fuel delivery (more or less based on RPM and TP). It also tends to run a bit rich with the MAF unplugged. Acceleration and cruise would improve if the MAF is having issues.

Example of someone who had to replace the MAF to get rid of his lean code: Engine code: "System too lean"
Alrighty, so I did notice when I unplugged it the rough idle was the same as when it's plugged in. That didn't change. As far as acceleration I didn't notice much of a difference.. I do recall cleaning it early on and when I deleted the CEL code it did stay off for some 40-50 miles before coming back on. Anytime after that when I cleared it the CEL came back on sometimes within a mile. So we just ordered a brand new one. We'll try it. Worst case scenario we have a new MAF that we know is good to go.
 

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buying a new maf is not a great choice; you should get a 2002 gt maf, and a tune to support it. same price, better metering.
 

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Discussion Starter #26 (Edited)
Keeping this post active so anyone having issues like mine can reference this post, as well as any info people share.

That being said...

So we’ve replaced the MAF.. cleared the code. It stayed away for a good 30 miles, and then came back. Same P1131. I’m clueless at this point as to what it could be, and wondering if the PCM is just throwing false codes. Also wondering if the rough idle isn’t related to any of this.

Parts replaced:
  • 02 sensor upstream bank 1 (what P1131 is supposed to be for)
  • EGR valve
  • IAC valve
  • vacuum hoses
  • MAF sensor
Checked the EVAP box, and canister. Both seem fine. I’m really starting to think the rough idle is transmission related (... yay..). Fuel economy improved noticeably since replacing the first three items right to where the car is rated. Spark plugs are also brand new.

Clueless at this point.
 

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The evap lines are shot, if you haven't replaced them.

They're leaking air, which is a vacuum, leak, and causing a rough idle.
 

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Discussion Starter #28
The evap lines are shot, if you haven't replaced them.

They're leaking air, which is a vacuum, leak, and causing a rough idle.
I think I replaced them... those hoses under the bumper going to the canister, and black box. Those are all brand new
 

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Do you have the means to do a vacuum leak test? Even an unlit torch and a can of propane would help.
 

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Discussion Starter #30
Do you have the means to do a vacuum leak test? Even an unlit torch and a can of propane would help.
I don’t, but im in contact with a guy with one of them smoke machines so we can do a vacuum leak test.

UPDATE:
So I took it to a mechanic who just took a quick look after I explained it all to him. Says the car appears to be running great, and suggested something may be causing the 02 sensor to not work right which might be giving me the code. He said without a proper diagnosis he couldn’t give me a certain answer, but when I asked about the PCM possibly being the problem he said it’s possible.

Neither of us think the car is actually running lean at this point. It’s MPG’s are drastically up (averaging 19 suburb/mountains/highway) , and both mechanics who have taken looks at it though they were brief said the engine seems to be running great.

Touching back on the one who ran his expensive scan tool that found a Bank 2 CAT being bad code, when the other codes dealt with Bank 1, he too suggested maybe the PCM is going bad and sending wrong codes. The Bank 2 cat code only appeared in that single scan tool while the others I’ve used only picked up P1131 and one regarding Bank 1 too lean.

The hunt goes on. Will continue to post as the hunt goes on until a cure is found so others experiencing similar issues can reference this thread.
 

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If you have a scan tool (if you've ever considered a tune, an XCal2 can interface and do all the live data streaming you need) you can also check to see the actual fuel trims and verify the O2 sensor is switching to find out if it is in fact the PCM.
 

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Discussion Starter #32
Latest updated:

We're throwing in the towel and bringing it to a shop. This morning it began throwing grey smoke out of the tail pipe, and still sitting here trying to track down this emissions issue is getting to the point where it's beyond what I can do at home. Maybe whatever went (piston ring, gasket, seal?) is related to whatever is causing bad emissions.

As always, I'll update the thread as this continue so future users can reference this post for solutions.
 

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Discussion Starter #33
Latest update:

The mechanic did all sorts of diagnostics on a really high end scanner, we did a pressure test (my rings are good to go!), and a smoke test.

Smoke test revealed the gasket between the Intake manifold and throttle body was bad.... I didn’t even know there was a gasket there.

Replaced it. Cleared codes. 17 miles later P1131 came back. That was the only vacuum leak the smoke test showed, and it was blatantly noticeable since the smoke we used was nice and thick making it easy to see. Not sure where to go from here chasing this code. Still getting a rough idle around 900rpm’s, and unsure how to proceed as this is driving me nuts now. Maybe I used the wrong gasket? The one I have from a Crown Vic 4.6 are significantly different while the one that came out of the T-bird is identical to the Doorman gasket I purchased new.
 

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What about an exhaust leak upstream of the Bank 1 oxygen sensor? That could draw air into the exhaust causing a false lean reading, then causing the PCM to enrich the air/fuel mixture to that bank. If the spark plugs in Bank 1 look normal and not white then the oxygen sensor is giving a false lean reading. Over-rich exhaust would show as smoke out of the exhaust but I'd expect it to be darker than gray. Yeah, because of the overlap in the valves an exhaust leak at either end of the exhaust manifold could have showed up during the smoke test, or maybe it only leaks when it heats up and expands.
 

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Discussion Starter #35
Much appreciated as I didn’t think of that at all. I’m gonna contact the mechanic I’m working with to see if that’s possibly what is going on.
 

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Discussion Starter #36
UPDATE:

So now the EGR I bought new decided to crap out on us, and the upstream bank 1 sensor isn't doing anything when you monitor it via hooking the car up to a scanning system. Bank 2 upstream is moving, and doing it's job like it's supposed to while bank 1 does read a fault. This kinda sucks given that 02 was the first thing I replaced, and it was a new part, but what are you gonna do right? Time to buy a ford factory one like I should've from the start. As for the EGR, we pressure tested it and it's not holding like it should. Thankfully it's under warranty, but I shouldn't have expected much from an Autozone/Duralast part.

I swear this has been the most PITA P1131 code to ever chase.

Will continue to post updates so future users who experience this wild goose chase can reference an eventual solution I hope. Other than the code, and rough idle car drives great. We've put around 4k miles on it since purchasing it.

ALSO:
I read in an old post on this forum someone suggesting Motor Honey to help with a car that burns oil.. We have what we believe are two bad valve stem seals in bank 1, (pressure test didn't find bad piston rings), and since using the Motor Honey our oil isn't burning much at all now.. In fact i haven't had to top it off in several days, and i check it after every time we take it anywhere. So.... MOTOR HONEY seems to be working!
 

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🤦

You will destroy your valvetrain with that crap; your oil pressure is going to be nil with thick oil in there.

That goo is for Chevy's will 300k miles and a 3-5mil bearing clearance.

Had you spent an instant searching here, you would have learned that the best thing to keep the hardened oil seals from leaking is a half-pint of transmission fluid in with the oil; exactly the opposite from motor honey.

If you doubt transmission fluids' seal swelling ability, put a drop on a plastic parts bag, and look at the result.

I use motor honey for pressing parts together; it has no value for our cars.

BTW, the oem vendor for O2 sensors was NTK; RA sells them.

I think... (sigh)

I'll just leave that there, I don't need to complete that paragraph...
 

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Discussion Starter #38 (Edited)
🤦

You will destroy your valvetrain with that crap; your oil pressure is going to be nil with thick oil in there.

That goo is for Chevy's will 300k miles and a 3-5mil bearing clearance.

Had you spent an instant searching here, you would have learned that the best thing to keep the hardened oil seals from leaking is a half-pint of transmission fluid in with the oil; exactly the opposite from motor honey.

If you doubt transmission fluids' seal swelling ability, put a drop on a plastic parts bag, and look at the result.

I use motor honey for pressing parts together; it has no value for our cars.

BTW, the oem vendor for O2 sensors was NTK; RA sells them.

I think... (sigh)

I'll just leave that there, I don't need to complete that paragraph...
I did spend a lot of time searching this website, and read nothing in regards to using ATF for that. In fact this is the first time I’ve ever heard anyone regarding any vehicle suggest that. Not saying you’re wrong, im just saying I’ve never heard of that.

Car is due for an oil change shortly anyway. Perhaps I’ll give it a try.

NTK is actually the 02 I put in there that failed. The one I pulled out was marked Ford, is identical to Bank 2, and was significantly different. Does NTK make a few different types?
 

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If you failed an o2 sensor in a short period of time, it's due to oil in the exhaust stream, a wiring problem, or an EEC problem.

I have three of these cars, and have never had that problem on any of them, with over 200k miles each. I have replaced the o2 sensors on all of them; two have wideband sensors too.

The valve stem seals leak, and can be replaced, but the effort is such that putting rebuilt PI heads on is a better option.

WTF does this mean? Pictures help.

The one I pulled out was marked Ford, is identical to Bank 2, and was significantly different.
All the ntk sensors are thinner in diameter than the bosch aftermarket replacements, which fail often.

ATF is a noted seal sweller; that's what it does, to a large extent.
Like I said, plastic parts bag and a drop for proof.
 

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Discussion Starter #40
Final comment regarding this chase:

Short answer:
gave up on it

- Half a bottle of motor honey with fresh 5w30 and the burning oil has stopped. Hasn’t burned oil in 12 or so days.

- replaced everything in the emissions system at this point. No new vacuum leaks. 02 on bank 1 is still not working. Car drives fine with a slight rumble like before at idle. CEL still on.

- car is now the “beater”... brought home a much nicer condition 1997’ T-Bird yesterday that is in excellent shape mechanically, and passed smog testing.

- no longer going to invest money into the Silver Bird at this point, and focus on making the White Bird our go everywhere car. Silver is my hill climbing work beater until it dies.

My apologies to anyone referencing this post for solutions as ultimately I was unable to fix this issue.
 
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