8 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHCold Start: Rough idle / Misfires (P0507, P0300)
Leading reported evidence
Check any obvious vacuum leaks
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
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Discussions that performed work without a confirmed outcome
1
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Performed · outcome unconfirmed · Original poster
Checked for any obvious vacuum leaks, from what I can tell all looks fine, I've had the air filter box in and out and looked all around but haven't done a proper smoke test as I don't have the equipment and no time to take it to a shop currently
Leading evidence: 'Check any obvious vacuum leaks' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check any obvious vacuum leaks' (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
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Performed · outcome unconfirmed · Original poster
Cleaned the MAF sensor with MAF cleaner (didn't look dirty, but figured why not)
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Discussions that contain suggestions
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Suggestion
Another thing to try would be to rent a fuel pressure gauge from a local parts store and check your fuel pressures then go from there.
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.
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Suggestion
Smoke testing would be great place to start, as drptphntr noted, smoke machines are fairly cheap and easy to get online.
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Suggestion
I bought a smoke tester and set of various size plugs for performing test for less than $100 on Amazon.
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
Check any obvious vacuum leaks
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
Checked for any obvious vacuum leaks, from what I can tell all looks fine, I've had the air filter box in and out and looked all around but haven't done a proper smoke test as I don't have the equipment and no time to take it to a shop currently
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
Here is a picture that someone else posted in a different thread that I saved and find useful as a reference of expected DME readings when using my Durametric.
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.
8 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: 20261026T174436Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Hey all, first post and unfortunately not the best way to start heh. Car is a 2004 996 C2 (manual), as of ~a month or two ago it's started throwing CEL codes and been having a very rough idle on cold start.
The most recent codes are :
P0300 (Misfire detection (total))
P0306 (Misfire cylinder 6)
P0303 (Misfire cylinder 3)
P0507 (Idle control at stop)
P0174 (Oxygen sensing adaptation idle range bank 2)
It's thrown other codes since this began (P0102 (Hot film MAF sensor), P0171 (O2 sensing adaptation range idle range bank 1)) however I've gone through a few cycles of trying to fix / clearing codes / driving, codes come back, etc. etc.
On cold start the RPMs rest ~1,100 (A/C off), however it's very "rough"/"chugging", and if I apply throttle up to ~2,500 RPM and let go, the RPMs crater to ~450-500 and the engine chugs and feels like it's going to die, until it stabilizes again around 1,100 RPM. Once the engine warms up after ~60 seconds it drops to ~900 RPM idle and sounds much better, drives great, no misfires, etc. and any subsequent "warm" starts seem fine.
So far I've:
Checked for any obvious vacuum leaks, from what I can tell all looks fine, I've had the air filter box in and out and looked all around but haven't done a proper smoke test as I don't have the equipment and no time to take it to a shop currently
Cleaned the throttle body (and "calibrated" it by let the key in the ignition not started for 60 seconds until I heard the clicks)
Cleaned the MAF sensor with MAF cleaner (didn't look dirty, but figured why not)
This all started happening after I decided to try the "Hemlholtz delete", which after the first drive with that installed it threw a CEL (P0507, P0171, P0174) so I removed it and have been having these issues since =/ not sure if related or coincidence but hey, trying to share all the info I can.
I bought a smoke tester and set of various size plugs for performing test for less than $100 on Amazon. Well worth the minimal investment, it paid for itself easily with the first vacuum leak it exposed.
Smoke testing would be great place to start, as drptphntr noted, smoke machines are fairly cheap and easy to get online. Definitely a great tool to have in the toolbox. I think (if someone knows for certain, please chime in) the O2 sensing range codes likely indicate a lean condition, which absolutely could indicate a vacuum leak or maybe a fueling problem. Do you have the ability to read live data on your car such as Durametric? I would check the O2 sensor readings as well as what your MAF is seeing. Another thing to try would be to rent a fuel pressure gauge from a local parts store and check your fuel pressures then go from there.
The issue has started since your last attempt at an "upgrade". U have messed something up. Most likely its a wiring or plug issue to the maf sensor or the sensor itself because thats the only thing u would have touched. U need a scanner to read the sensor output and go from there.
Yup great point on the smoke machine, I went ahead and bought one on Amazon today, will sort that out and test when it comes in =).
I do have a Durametric, for the O2 and MAF sensor reading, what are the expected values? Will also take a look into renting a fuel pressure gauge, thanks for the suggestion =)
Yeah I figure there is a good chance it's not a coincidence heh. I'll be taking a look at the MAF values with my Durametric when I get the chance, do you know what the expected reading would be?
Here is a picture that someone else posted in a different thread that I saved and find useful as a reference of expected DME readings when using my Durametric.
