8 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHHigh Long Term Fuel Trim, potential problem?
Leading reported evidence
Check mass air flow sensor
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
I checked my MAF sensor with the engine off, ignition on and got 1.03 volts and engine on and idle at 1.318 volts.
Leading evidence: 'Check mass air flow sensor' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'maf due' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check mass air flow sensor' (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.
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
I also changed my O2 sensors, but that didn�t have much effect.
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
I've recently smoke tested the engine and replaced all the places where there was a vacuum leak.
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
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Performed · outcome unconfirmed · Original poster
I also had bad catalytic converters so I replaced those along with 4 new O2 sensors.
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
I've recently smoke tested the engine and replaced all the places where there was a vacuum leak.
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
maf due
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 · Original poster
I didn't think it was the MAF due to the voltages being in range, but after charting the MAF flow rate, RPMs, and throttle position it does look like the MAF responds incorrectly in a few situations.
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: 20261026T155324Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
I have 2003 C2 996 with 157,000 miles on it. I'm trying to determine if my somewhat high fuel trim is a problem. I've recently smoke tested the engine and replaced all the places where there was a vacuum leak. Oil filler neck, manifold elbow and resonance tube. None of the hard plastic vacuum lines or elbows were leaking so I didn't replace any of those. I also had bad catalytic converters so I replaced those along with 4 new O2 sensors. As well as new spark plugs and coil on plugs.
The car runs great, pulls super hard and idles perfectly with the A/C on. When I turn off the A/C the idle becomes a bit rougher it almost seems like there's a miss, but nothing is showing on my generic OBD reader. No misfires detected, all emissions tests have passed and no pending or current codes. Because of the slightly rough idle with the A/C off I decided to look through the live data on my scanner. That's when I noticed my LTFT was sitting at ~8% on bank 1 and ~5% on bank 2. STFT seems to stay around -1% to 3% most of the time. However, if I snap the throttle STFT will sometimes go to ~10% - 12% before returning to 0%. I checked my MAF sensor with the engine off, ignition on and got 1.03 volts and engine on and idle at 1.318 volts. These numbers seem to be in range from what I can tell online.
Of course I want my LTFT to be as close to 0 as possible, but I know there's a bit of a normal range. I wouldn't even think about it if it wasn't for the somewhat rough idle without the A/C. With A/C on the engine RPMs pick up a bit and the idle is absolutely smooth as silk.
Do the LTFT numbers above point to any potential issues? If not, is it normal to have a rougher idle with the A/C off then with it on?
Thanks in advance!
When I first bought the vehicle, I had similar issues with LTFT being on the high side. I performed the same diagnostic checks as you, as well as verifying MAF voltage. A new Bosch MAF resolved my issues. The PO had installed a K&N intake (which is now in the trash) and I now have an oem 3.8 intake as well.
My LTFT numbers were pretty high, even though my engine was running great. I also changed the MAF and it brought the numbers down quite a bit. I also changed my O2 sensors, but that didn�t have much effect. My LTFT is still a bit high. I may change my fuel injectors next.
Thanks for the feedback. I'll try a new MAF. I didn't think it was the MAF due to the voltages being in range, but after charting the MAF flow rate, RPMs, and throttle position it does look like the MAF responds incorrectly in a few situations. I'll post back here once I have a new one installed.
I wanted to follow up on this in case anyone else runs into the same issue. A new MAF fixed both the high fuel trims and the rough idle without the A/C. I've driven over 100 miles and my LTFT's are around 1 on bank 1 and 0 on bank 2.
The diagnostic info in the Porsche service manual wasn't enough to point out a failing MAF because the voltages were in the range specified.
Thanks sweet victory and wsrgklt for the input!
