15 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHBoth banks lean codes 171 & 174
Leading reported evidence
Replace aos/breather hose/vacuum lines
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
I think you didn't hook something up right when you replaced the AOS/breather hose/vacuum lines.
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Suggestion
check better for a vacuum leak, lean means too much air after MAF, I would guess the plastic vent for AOS (runs under intake) has a crack in it somewhere or is not completely on the ends.
Leading evidence: 'Replace aos/breather hose/vacuum lines' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check better' (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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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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Performed · outcome unconfirmed · Original poster
I have been spraying starter fluid in different areas today and it reved up when I sprayed the 1st bank intake manifold gasket so i tightened all those bolts.
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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Suggestion
check better for a vacuum leak, lean means too much air after MAF, I would guess the plastic vent for AOS (runs under intake) has a crack in it somewhere or is not completely on the ends.
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 · Original poster
I checked all connections & sprayed some starting fluid on all that I could get to, but did not notice any change in rpm's.
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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These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
Check better
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
check better for a vacuum leak, lean means too much air after MAF, I would guess the plastic vent for AOS (runs under intake) has a crack in it somewhere or is not completely on the ends.
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
I did just replace the AOS & breather tube (long one) and double checked everything because I knew it would be a pain to access once I put the engine back in.
Discussions that performed work without a confirmed outcome
1
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Performed · outcome unconfirmed · Original poster
I have been spraying starter fluid in different areas today and it reved up when I sprayed the 1st bank intake manifold gasket so i tightened all those bolts.
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
The "too lean" implies that the readings the DME is getting out of the oxygen sensors don't correlate to how much fuel should've been used according to calculations made based on load/airflow reading, etc.
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.
15 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
After pulling engine & transmission & replacing IMS bearing, AOS & breather hose, vacuum reservoir, plugs,& oil filler tube I have codes of 171 & 174- both banks lean.
I checked all connections & sprayed some starting fluid on all that I could get to, but did not notice any change in rpm's. I kind of avoided spraying much starting fluid around the alternator- didn't want to torch anything.
After 5-6 weeks of not being started the car sounded rough at first start
& sounded like what Philooo described on his bad fuel post, but starting running close to normal after a few drives.
I cleared the codes a few days ago, but just checked and they came back. Should I not run the car with these codes? Any clues on what to look for or do to run this down?
check better for a vacuum leak, lean means too much air after MAF, I would guess the plastic vent for AOS (runs under intake) has a crack in it somewhere or is not completely on the ends. Given the work you just did that is the most likely culprit.
Also check to make sure both manifold tubes have the rubber connections all the way on and tight.
Thanks for the ideas- I will try them all.
Ivangene- the power seems fine high and low rpm's now. At first start up it wondered and stalled a few times- but maybe that is normal when car has not been started for 5-6 weeks and disassembled.
Is it OK to run the car with these codes? Don't worry if it blows up on your advice, I have been driving for a week now.
Also, do most spray starting fluid at the connections and vacuum lines to find the leak? That is what I have done with all my other cars, but they didn't have the engine packed in a little suit case with the alternator sitting in front.
In my limited knowledge about engines: Running rich robs power but its OK. Maybe it will kill CATs prematurely. Running the engine lean will create serious problems if driven long term.
If it drives fine, it's probably OK. The 996 is set to run -like many other modern cars- (and will do so just fine) even without the MAF plugged in, so I don't think you're going to hurt anything to drive it for the time being. The "too lean" implies that the readings the DME is getting out of the oxygen sensors don't correlate to how much fuel should've been used according to calculations made based on load/airflow reading, etc.
It sounds like a vacuum leak to me as well, and you should look at things that would affect both banks. If it was a larger leak, it would likely impact higher rpm operation to some degree as well. I would concentrate on things that were taken apart recently.
Could be low fuel output when the computer is trying to put as much out as possible to prevent lean. Pump, injectors or fuel bad. I'd stay away from not driving it for extended priods like the 4-6 weeks you just did and put some new gas in there. You might have to labor through driving the tank till near empty to be sure you get all fresh fuel. I'd dump some injector cleaner and fuel stabilizer in before topping off if the parking the car for long periods isn't avoidable.
I think you didn't hook something up right when you replaced the AOS/breather hose/vacuum lines. It's sucking in air causing a lean reading.
Rick
99 996C4
87 944S
I think I found it. I have been spraying starter fluid in different areas today and it reved up when I sprayed the 1st bank intake manifold gasket so i tightened all those bolts.
Now it revs up when I spray the AOS area, I just can't figure out how to get back there yet. I did just replace the AOS & breather tube (long one) and double checked everything because I knew it would be a pain to access once I put the engine back in.
You where right.
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