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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHIdle Kinda Steady but Misses 1999 996 NB
Leading reported evidence
Check any codes
Suggestion or failed attempt
No successful repair reported for this finding.
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1
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Read evidence and context
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Leading evidence: 'Check any codes' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check any codes' (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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Suggestion
I would suggest cleaning the idle control value or replacing it...
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Suggestion · Original poster
Do not know if the AOS was replaced before or at the rebuild stage.
Replace coil packs & spark plugs, do a compression
Suggestion or failed attempt
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
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Suggestion
Change coil packs & spark plugs, do a compression test while you are it.
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11 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
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I recently purchased a 1999 996 with 90,000+ miles. Engine was rebuilt by the seller about 300 miles ago. Runs great at all speeds. At idle the needle stays steady but there is a minimal but noticeable roughness.
Do not know if the AOS was replaced before or at the rebuild stage. When I pull off the oil cap there is vacuum resistance but not major and the idle remains steady. No oil smoking and no warning lights. Other than the AOS, could it be something as simple as a coil, plug, injector, or? Is it the AOS. This is my first 911 and am not sure if this idle is expected and one of those things I need to get used to in a 15 year old car.
Thanks for your expertise and advice.
Cheers.
"roughness" can be very subjective, especially when trying to describe it over words. What's your idle rpm's at? And were any of your previous cars inline motors like a Honda or BMW by chance?
A failing AOS would use some amount of oil and could produce smoke out the exhaust.
Any idea of the age of the coil packs and spark plugs?
Apart from coil packs, most idle roughness is the fault of worn engine mounts. They're a relatively easy DIY if you have a floor jack and a socket set.
How many miles on your Porsche cinellipro, and can you see RPM fluctuations with your tach needle, at idle after the car is warmed up ? Any other pics of your white Porsche?
I do not know the age of the coils or motor mounts. RPMs are steady at about 750 at idle. The needle does fluctuate but only about 1mm. The car has 90300.
If your engine mounts have not been changed the fluid in one or both may have leaked out. That would cause light vibration and or roughness, especially at idle. I would change them, @90k they are near their end of life if not dead.
I did mine at 60K and noticed less vibration.
If your motor mounts are that bad, a typical visual indicator is that one exhaust tip hangs lower than the other. If the engine was just rebuilt 300 miles ago, I would think bad mounts would have been replaced. I swapped mine out at 83k and they were stretched out a fair bit and it was obvious. Are you able to check for any codes ?
Try from the cheapest to the most expensive. Clean maf sensor, iddle control valve and give it a good fuel additive. Inspect the motor mounts like everyone says. Change coil packs & spark plugs, do a compression test while you are it.
The '99s do have a bit of a "rough" idle to them. Not like a shaking type of rough, but more of a fluctuating kind of idle, especially if the climate control is on. My car will regular fluctuate 100rpm up or down, especially when it's cold.
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