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Weird problem: '99 996 C2; hissing sound and throttle/idle is high

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2 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis

THIS DISCUSSION / SOURCE-DERIVED OVERVIEW

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YOUR RESEARCHWeird problem: '99 996 C2; hissing sound and throttle/idle is high

Leading reported evidence

Replace iacv

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
- Replaced the IACV
Original post Read captured discussion
Weird problem: '99 996 C2; hissing sound and throttle/idle is high

Read full discussion summary

Leading evidence: 'Replace iacv' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'power brake vac line' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Replace iacv' (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.

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

Compare 2 other evidence results

power brake vac line

Suggestion or failed attempt

No successful repair reported for this finding.

0
Identified cause: 1
Suspected cause: 0
Reported fixes

Read evidence and context

Discussions that suspect a cause: 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.

Suspected cause
Probably the power brake vac line.
Original post Read captured discussion
Weird problem: '99 996 C2; hissing sound and throttle/idle is high

Smoke-test would verify

Suggestion or failed attempt

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
Its a know vac leak point and a smoke test would verify.
Original post Read captured discussion
Weird problem: '99 996 C2; hissing sound and throttle/idle is high

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.

Replace iacv

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
- Replaced the IACV
Original post Read captured discussion
Weird problem: '99 996 C2; hissing sound and throttle/idle is high

Smoke-test would verify

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
Its a know vac leak point and a smoke test would verify.
Original post Read captured discussion
Weird problem: '99 996 C2; hissing sound and throttle/idle is high

Reported and suspected causes (1)

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

power brake vac line

No successful repair reported for this finding.

0
Identified cause: 1
Suspected cause: 0
Reported fixes

Read evidence and context

Discussions that suspect a cause: 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.

Suspected cause
Probably the power brake vac line.
Original post Read captured discussion
Weird problem: '99 996 C2; hissing sound and throttle/idle is high

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: 20261026T105141Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources

POST 1 / ORIGINAL POSTEROriginal post

Weird problem: '99 996 C2; while letting off the gas, particularly at slower speeds in a parking lot, a hissing sound near the throttle body can be heard and the car seems to maintain a little throttle for about another second before dropping. The idle is between 900-1000 which is high. I'm thinking a vacuum leak so I have been diagnosing everything for the past month or so. I haven't smoke tested it yet but I've done the following maintenance. - Replaced the IACV - Checked all my vacuum lines, I have no AC or Pwr steering so I can get all the way to the back and underneath the intake manifold easily. There are some vacuum lines that I have just blocked off with screws. - SAI system is deleted with block off plates, car is on a ROW DME program - Spark plugs, tubes and coilpacks are all less than 1k miles on them. - Oil filler cap is brand new - Coolant cap is brand new - Unplugged the MAF and the car idles the same - PCV valve is new with a new O-ring - IPD throttle body installed When facing the engine there is a hissing noise coming from the rear drivers side of the engine. When I turn the key off it keeps going for about a second and a half. That could just could be the intake, but I have a stock box and filter so I don't know. When I did my alternator last night I inspected everything on that side, there are no open vacuum lines. I have no codes, the car runs very strong. No hesitation, there is pressure when removing the oil cap. What do you guys think?

POST 2Original post

Probably the power brake vac line. Its a know vac leak point and a smoke test would verify.

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