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Rough running engine - no codes, no CEL

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Original source
2 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW

Discussion summary

YOUR RESEARCHRough running engine - no codes, no CEL

Leading reported evidence

Replace plugs and coils

Performed · outcome unconfirmed

No successful repair reported for this finding.

0
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 performed work without a confirmed outcome
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.

Performed · outcome unconfirmed · Original poster

The plugs and coils have been replaced for other reasons and I've used Liqui-Moly injector and valve cleaner several times with no effect.

Original post Read captured discussion
Rough running engine - no codes, no CEL
Read full discussion summary

Leading evidence: 'Replace plugs and coils' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Replace plugs and coils' (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.

Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.

Read captured replies

1 matching discussions · 2 captured posts examined · 0 partial discussions

Compare 3 other evidence results

Replace twice in my ownership

Performed · outcome unconfirmed

No successful repair reported for this finding.

0
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 performed work without a confirmed outcome
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.

Performed · outcome unconfirmed · Original poster

Oil's been changed twice in my ownership but I've not used any lubrication modifier or anything like Sea-Foam to mess with the oil.

Original post Read captured discussion
Rough running engine - no codes, no CEL

Use liqui-moly injector and valve cleaner several times

Performed · outcome unconfirmed

No successful repair reported for this finding.

0
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 performed work without a confirmed outcome
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.

Performed · outcome unconfirmed · Original poster

The plugs and coils have been replaced for other reasons and I've used Liqui-Moly injector and valve cleaner several times with no effect.

Original post Read captured discussion
Rough running engine - no codes, no CEL

Run bit rough, like an old v8

Suggestion or failed attempt

No successful repair reported for this finding.

0
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
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

The engine has always run a bit rough, like an old V8 with a bigger cam than stock.

Original post Read captured discussion
Rough running engine - no codes, no CEL
Frequently discussed actions (4)

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

Replace plugs and coils

No successful repair reported for this finding.

0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that performed work without a confirmed outcome
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.

Performed · outcome unconfirmed · Original poster

The plugs and coils have been replaced for other reasons and I've used Liqui-Moly injector and valve cleaner several times with no effect.

Original post Read captured discussion
Rough running engine - no codes, no CEL

Replace twice in my ownership

No successful repair reported for this finding.

0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that performed work without a confirmed outcome
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.

Performed · outcome unconfirmed · Original poster

Oil's been changed twice in my ownership but I've not used any lubrication modifier or anything like Sea-Foam to mess with the oil.

Original post Read captured discussion
Rough running engine - no codes, no CEL

Run bit rough, like an old v8

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

The engine has always run a bit rough, like an old V8 with a bigger cam than stock.

Original post Read captured discussion
Rough running engine - no codes, no CEL

Use liqui-moly injector and valve cleaner several times

No successful repair reported for this finding.

0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that performed work without a confirmed outcome
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.

Performed · outcome unconfirmed · Original poster

The plugs and coils have been replaced for other reasons and I've used Liqui-Moly injector and valve cleaner several times with no effect.

Original post Read captured discussion
Rough running engine - no codes, no CEL
Coverage and how to read this overview

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.

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

  • Rennlist: 1 discussions

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

0 acknowledgements have no verified action link; they do not establish a repair result.

Generation: 20261026T124918Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources

POST 1 / ORIGINAL POSTEROriginal post

I have a 2003 C4S with the X51 package that I purchased last November. I use the car as my daily driver so I've put about 11k on it since purchasing. The engine has always run a bit rough, like an old V8 with a bigger cam than stock. Kind of a smooth - shudder - shudder - smooth cadence. The motor pulls hard but I feel the shudder even free rev-ing the engine and trying to hold a steady RPM. At idle, when it's doing the shudder thing, the RPM's jump imperceptibly on the tach but I can see them bounce through the OBD reader. The plugs and coils have been replaced for other reasons and I've used Liqui-Moly injector and valve cleaner several times with no effect. There are no codes in the ECU, no misfire or cam or injector codes at all. My local Indy repair shop thinks it may be the vario-cam not fully disengaging. Oil's been changed twice in my ownership but I've not used any lubrication modifier or anything like Sea-Foam to mess with the oil. Any ideas? The vario-cam thing seems likely but before I spend that kind of time or cash I'd like to be sure.

This is a source reference. Confirm exact model applicability in the original material.