Cayenne S 957 Rough idle at cold start

[TomBelgium]

Hi,

Since a few weeks I am the owner of a Cayenne S 957 4.8 from 2008. But I notice that the car struggles to start after standing a few hours.
When I try to start it in the morning it takes a few seconds to start and then it idles quit rough. It seems to misfire in some cylinders. When I press the accelerator to 2000rpm for a second or 2 it goes to a "normal" idle and the shaking and rough idle are gone. No error codes are shown on the dash or Piwis tester.
There is no unusual noise coming from the engine and it had a new battery last week (unfortunatly that didn't fixed the issue).

Anybody who had the same problem before and has any ideas how to fix it? It drives great it is just the rough idle at cold start that is not right.

Kind regards

Tom

[JFP in PA]

Unfortunately, without codes or other "real time" data capture from the vehicle, this is rather difficult to diagnose remotely.  Is it possible for you to capture data while this is happening?

[TomBelgium]

Yes i can, I have a piwis tester at home. 

[TomBelgium]

But as it doesn't give any fault codes i don't know what the problem could be. Also HPFP values seems ok..

 

[JFP in PA]

It doesn't have to throw codes to run poorly, we see cars from time to time that were barely running, but free of codes; these are what separate those that understand diagnostics from those that throw parts at the problem.

[TomBelgium]

I also forget to mention that when i put the cayenne in Drive or Reverse it also goes to a stable, normal idle.

[TomBelgium]

On 7-7-2017 at 4:33 PM, JFP in PA said:

Unfortunately, without codes or other "real time" data capture from the vehicle, this is rather difficult to diagnose remotely.  Is it possible for you to capture data while this is happening?

I took pictures of the engine data before and after starting the car. What data should i upload here?

[JFP in PA]

Fuel trims would be a good place to start.................

[TomBelgium]

It seems like my actual value is following my setpoint high pressure value when driving or idling. But only after the rough running is over.

It doesn't keep the high pressure in the rail, i only got around 4 to 5 bar when the car is turned off. I believe it will be a valve in my HPFP as the low pressure (which should be around 5.5 bar) is maintained (it is normal to drop 1 or 2 bar in a couple of hours).

 

[nasocbr]

Hi

 

Same situation here. Was it the HPFP?

Edited January 11, 2018 by nasocbr

[Pxwguad]

I spoke to my Porsche dealership about this and they told me that it’s normal on a cold start and that that’s how they heat up the catalytic converter quicker to meet emissions standards