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996 slightly erratic idle.

APL911

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15 Aug 2017
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305
Evening all.

I've done a search but can't really find a conclusive answer.

My 996.2 c2 manual has a slightly erratic idle.
Oil pressure is good etc.

It idles around 800rpm and shuffles up and down.

I'm nervous it could be the IMS bearing.

Any insight or advice would be great.

Thanks

Antony.
 
MAF sensor perhaps my 997 did what just what you describe I took it out and used some sensor cleaner on it ,sorted child's play well it must be I managed it :thumb:
 
IMS bearing .. erm .. no .. it still runs !

Seriously though .. its not the IMS .

Air leak is the most obvious followed by clean the throttle valve then check for fault codes and what the mixture adaptions are .. done with a tester .

Post results if you have a tester .
 
...a question for the technicians; using an obd can one confirm that the AOS and vacuum lines are good?
My non technical brain is inclined to think that a strong idle vacuum reading is a sign of a healthy engine and AOS, and non leaky vacuum lines?
Is my thinking correct?

For example my 996 Gen 2 shows around 24 ish (idle intake vacuum) on a cold idle which is about the same as my newer BMW 630i....
 
I had erratic idle in my C2 about a year ago. I had a few things done at the same time / Crank Angle Sensor / Breather Hose / Battery.
Breather hose was full of splits....maybe worth a look.
Idle is a lot better.
Jim.
 
The 996 is VERY sensitive to air leaks - any "erratic" behaviour is almost certainly vacuum or general air leak related..... its "consistent" behaviour you need to worry more about..... but even then, it's not always an IMS bearing about to explode and end all life on the planet (despite what various magazine and online articles have said over the years)
 
So I'm changing the air filter tomorrow and fitting the DT CAI.

I'll clean the throttle valve. Can I use carb cleaner on the MAF as well or just give it a wipe down...?
 
IIRC carb cleaner is a no no as is a wipe down I sure I used a sensor cleaner that will not leave a residue :thumbs:
 
Just been into the man cave I used CRC sensor cleaner :thumb:
 
holy thread resurrection!

chasing vacuum leaks - there are many, many pipes in that engine bay, many of which are almost inaccessible :(

so is there a common culprit to check first? (Photos / links would be helpful!)

symptoms are:
a very slight idle lumpiness
some hesitation below 2000rpm.

and where do you get CRC cleaner from? :D
 
Thats a bit of a needle in a haystack question im afraid .. i can think of many things from a maf sensor to a slight misfire that would cause this .

First things first do you have a tester ?

We need fuel adaptions to see if there is an air leak , we need the rough running or misfire section .. we need the lambda sensor state .. is it switching correctly .

To answer your question though .. no there is no set air leak and the car will compensate for any small air leaks reguardless .. it will richen up the mixture and therefore eliminate the problem basically .
 
Thanks DeMort
I've ordered an OBD reader so I'll let you know when I have some readings :thumb:
 
FWIW, although I'd not really had cause for concern the idle is a lot smoother on mine since fitting new coil packs (and plugs).

The originals although not that old (replaced at OPC about 5-7 years ago, maybe 20k miles or something from memory) were all degrading to some degree. A couple had noticeable cracks when removed but almost all of them showed some very slight hairline splits beginning when cleaned up/checked over. Certainly worth replacing whilst you're in there - I think the current/updated BERU packs are circa £20/30 each. Didn't have any misfire codes on a basic OBD reader - perhaps the correct Porsche diagnostics would help pinpoint any issues a bit easier?

Quite a common issue I understand due to their proximity to the exhausts and crud/damp from the rear wheels/underneath. I'd probably want to check/rule out the basic stuff/service items first 8)
 
FWIW i fixed mine by simply cleaning the throttle valve with some carb cleaner. :thumbs:
 

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