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epic MOT emissions fail... lambda? - Page 1 - 911/Carrera GT - PistonHeads UK

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10 captured repliesPartial discussion capture · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW

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YOUR RESEARCHepic MOT emissions fail... lambda? - Page 1 - 911/Carrera GT - PistonHeads UK

Leading reported evidence

Run very lean at fast idle

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Suggestion

It could be an air leak that is causing the engine to run very lean at fast idle.

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epic MOT emissions fail... lambda? - Page 1 - 911/Carrera GT - PistonHeads UK
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Leading evidence: 'Run very lean at fast idle' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Run very lean at fast idle' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.

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Test lambda reading is off the charts

Suggestion or failed attempt

No successful repair reported for this finding.

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Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context

Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.

Discussions that contain suggestions
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0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.

0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.

Suggestion · Original poster

Especially the 2nd fast idle test, lambda reading is off the charts.

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epic MOT emissions fail... lambda? - Page 1 - 911/Carrera GT - PistonHeads UK
Frequently discussed actions (2)

These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.

Run very lean at fast idle

No successful repair reported for this finding.

0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1

0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.

0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.

Suggestion

It could be an air leak that is causing the engine to run very lean at fast idle.

Original post Read captured discussion
epic MOT emissions fail... lambda? - Page 1 - 911/Carrera GT - PistonHeads UK

Test lambda reading is off the charts

No successful repair reported for this finding.

0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1

0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.

0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.

Suggestion · Original poster

Especially the 2nd fast idle test, lambda reading is off the charts.

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epic MOT emissions fail... lambda? - Page 1 - 911/Carrera GT - PistonHeads UK
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Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.

10 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.

  • PistonHeads: 1 discussions

0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.

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Generation: 20261026T181445Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources

POST 1 / ORIGINAL POSTEROriginal post

I'm not really familiar on causes for this. Car runs perfectly (996.2, 3.6), rebuilt 3k miles ago, included new cats and exhaust backboxes. No CEL, no hesitation, no symptoms... apart from MPG's. struggling to get past 25mpg. Especially the 2nd fast idle test, lambda reading is off the charts. Am I guessing right one of the lambdas may be on the way out ? How can the two attempts be so different? I mean, every reading is not even close to attempt 1.. Edited by cvega on Tuesday 10th October 09:16

POST 3 / ORIGINAL POSTEROriginal post

Topgear 200 cell ones. Car was warm (took it down for a blast on the Mway).

POST 4Original post

Cats are most likely causing the readings. Mate has a rebuilt C4s with 200 cel cats and had the same problem. Just find a friendly MOT place.

POST 5Original post

Or fit some O2 sensor extensions : https://www.design911.co.uk/porsche/996--911--1997...

POST 6 / ORIGINAL POSTEROriginal post

okay, a bit surprised as Topgear states they are direct replacements for OE cats.

POST 7Original post

It could be an air leak that is causing the engine to run very lean at fast idle.

POST 8Original post

due, often to bore size of the exhaust and how far the lambda probe goes into a 911 exhaust, air get sucked back and causes a fail. if the tester will block the tailpipes in the exhaust with rags, it will pass

POST 9Original post

Maybe pulling air somewhere? Or as stated above block up tail pipe if tester will and lamba reading will come right down

POST 10Original post

bevsy said: Maybe pulling air somewhere? Or as stated above block up tail pipe if tester will and lamba reading will come right down The 200 Cell HJS cats on the Cargraphics manifolds fitted to my 3.8L Cayman S failed twice first after 7k miles then after another 20k miles. They tend to break away at the edge of the cylinder as pictured. HJS provide exhaust manufacturers with a two year warranty from date of HJS manufacture. Luckily my failures were within this time limit else £500 per side.

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