10 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHWhy is my 996 getting 12.5 MPG?
Reported or suspected cause
nut behind the wheel
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
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Leading evidence: 'nut behind the wheel' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'nut behind the wheel' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Disconnect negative battery lead' (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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Performed · outcome unconfirmed
When i purchased the car i reset the AVG MPG in the cluster.
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Suggestion
Try disconnecting the negative battery lead for 30 minutes to reset the DME, then do some drive time to establish new values on the new plugs/coils.
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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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.
10 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T103553Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Which plugs and coils did you replace with? Why did you replace the plugs and coils? Try disconnecting the negative battery lead for 30 minutes to reset the DME, then do some drive time to establish new values on the new plugs/coils.
It's probably due to aging 02 sensors. They are designed to run for at least 120k miles under normal circumstances. But sometimes will last longer( sometime not), but the aging will slow response time and bias the fuel trim.Get you a bluetooth (or wifi for IOS) OBDII adaptor and a phone app and read your fuel trims. Fuel trims should be near zero , if too far from zero means something is amiss and is being compensated for.
How many miles are on your engine?
I have had my car since 2000 and 4,000 miles. Around town it has always gotten 12-14 mpg. On the highway cruising at 80+ I can get 25-28 MPG. So if you are getting 12.8 mpg around town it does not surprise me.
Was the battery reset when the coils and plugs were changed?
i only ask because doing so resets the AVG MPG calculations. Allow me to explain. My car is typically only driven on the highway back and forth to work 1 day a week. Its 50 miles round trip and all highway. When i purchased the car i reset the AVG MPG in the cluster. Right now it reads AVG MPG as 22. This is because the last time i reset it it has only seen the avg high mpg from the highway. If i were to clear it again and do more local in town driving it would instantly read very low MPG AVG.
At work we see this complaint from people who do a lot of highway type driving. Then they come in and we do some repair that requires a battery reset. Then for the next few days or even weeks the AVG MPG is messed up until they put some time on the car for a better calculation to see a true avereage. Hope that makes sense.
