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Old 07-16-2008, 05:00 PM   #1
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Rough Cold Idle

Any ideas as to why when cold the idle is rough? Once temp gets close to 180 degrees it smooths out?
Here's what I did that preceded the symptoms:
De-snorkled
Ran 1 tank with Regular.

Have since re-snorkled
Ran at least 3 tanks with normal premium gas.


Cleaned the throttle body, which initially remedied idle problem (for a few cold starts) and then went back to rough while cold idle.

Particulars: 2002 Boxster S, Tiptronic, 66K miles.

Any ideas?

Joe
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Old 07-16-2008, 05:17 PM   #2
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Try using only premium/supreme... the best you can buy from Cheveron or Mobile are usually the cleanest fuels... When was the last time you had your sparkplugs changed?
Also look under the engine on the passenger rear side of the engine for oil leaks, if theres fresh looking oil drips on that side of the engine then you probably have a ripped bellows tube on your AOS which would result into a vaccum leak and cause your idle to be rough at different times.
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Old 07-16-2008, 07:10 PM   #3
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Had the 60K service done at Porsche. Don't the plugs get changed then?
Will look for oil leaks tomorrow am.
Thanks,
Joe
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Old 07-17-2008, 02:55 AM   #4
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you didn't mention it, so i thought i'd ask...is your check engine light on? you could've also just gotten a bad tank of gas (maybe a little water in it). also, when you put that regular in there, the lower octane fuels burn slower, maybe causing you to foul out an O2 sensor, or possibly a spark plug (even if the plugs were just replaced).
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Old 07-17-2008, 05:12 AM   #5
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Another quick low cost solution is to clean the Mass Air Flow sensor. My Carmy has 90K miles on it and when I cleaned the MAF it idled like a brand new car.

Search this site for MAF. You will need a special torx bit (tamper proof) tool to remove the sensor. I did it on my Boxster and it took about 20 minutes.

-Steve
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Old 07-17-2008, 07:07 PM   #6
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CEL is not on. Regarding the O2 sensor, how would I know if it was the case that the regular fouled it out?
Oh, by the way, forgot to add another recurring situation since cleaning the throttle body, emits a large plume of smoke everytime I do a cold start. Less in the morning, more when leaving work around 6ish.
CJ, no drips on either side.
Will try cleaning the MAF this weekend.
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Old 07-20-2008, 10:56 AM   #7
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Update.
Cleaned the MAF. Still no difference in cold idle.
More info on symptoms:
Idle is steady at around 1K, then settles to 800. But the engine is running rough (does a little 'hunting', range 750 - 800 for the duration until it hits the magic temp). Car noticeably shakes/vibrates.
As soon as the temp reaches just past the 2nd hash mark, 100 degrees being the first, the idle settles to 800 and runs smooth like one would expect.
Considering taking it to the dealer and let them diagnose the problem and then dim.
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