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Hi all,


I have a cayenne turbo 2005, 140 000 miles now, it’s my daily.

It’s a little rough when idling, but fine when driving (all power, everything ok). I also have the issue when I am driving and stop to a red light, the car idle a little lower before coming back at normal idling (from what I understood it is maybe the engine hydraulic mount).

What I change in the last 3 months:

- spark plugs (I had some random multiple misfire (P0300) and some on some cylinders (P302, P304…)

- spark coils (due to misfire)

- driver side gas pump (died and had me stuck on a parking lot)

- valve cover gaskets (leak)

- upper engine mounting arm (needed to be replace)

- cleaning of throttle body

- cleaning of both MAF


I still have rough idle….

sometime I have an engine light on the dash, 3 or 4 time, once a month, and I have 02 sensor error. Can be reset with duramteric or reset by itself too.


So I check with my durametric again yesterday and this is what I have:

-P0431 catalyst system efficiency below (bank 2)

-P0300 random multiple cylinder misfire

-P0302 cylinder 2 misfire

-P0304 cylinder 4 misfire

-P0308  cylinder 8 misfire

-P0421 catalyst system efficiency below (bank 1)


I don’t know where to start to look now. I googled it and did not find anything. If someone has an idea I am open to any suggestion!

Thank you

Edited by skalex
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Following. Similar issues. I have done a lot of the same maintenance. I also found a few vacuum leaks which I fixed. 08 CTT



You might want to check out the "stutter and hesitation" thread, as it has some good info although no solution for us.


Sent from my iPhone using Tapatalk



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2 hours ago, skalex said:

Thank you for your feedback. I will look at this post. hopefully it will help.

I already looked at a lot of post but nothing helped me yet...


Look for vacuum leaks I would suggest first at 140,000km and 12-13 yrs would be likely to find some cracked and brittle pipes and hoses. 


You have changed all your coils right? What did the old spark plugs look like? Any pictures. 


The cat code are worrying. If not due to the misfires which they may well be failed/melted blocked cats are expensive to replace. 

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thanks for the feed back.

I will start to look at the vacuum leak, but not easy without a smoke test equipment.

I changed all coils and spark plugs a month ago. About the old one, I did not really check, because I was thinking my problem was coming from the spark plugs/coils (misfire codes).

The cat issue doesn't excite me... but I have bank 1 and bank 2, what is the chance to have 2 cat dead in the same time....

I am thinking maybe try to change the O2 sensors, but $200 to $300, I would like to be a little more sure it can be the problem before i change them.

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3 minutes ago, skalex said:

I agree :) 

O2 sensor post cat won't cause misfires. Start at the likely misfire causes.

 Make a home made smoker from 1 litre bottle, air compressor set at 10psi and some cigars easy peasy. Use the map sensor port. Disconnect the maf pipes from the air boxes and thick freezer food bag and duck tape them tightly this will keep your smoke inside. 

I posted picture of this Hill Billy method before and it works pretty good. Youtube it. 

Another train of thought is blocked injectors and or fuel delivery issues. Your old cats can't cope with the unburnt fuel in the exhaust caused by the misfire events that's what the code actually is telling you, not that the cat is necessarily knackered and inefficient. 


Have you check your AOS diaphragm and 3 way check valve? Pipe connection to bottom of Y pipe and throttle body gasket. Even the Y pipe is known to split but that would normally give sound when on boost. 

Whats your boost gauge say full throttle?  


Not to offend but spark plugs tightness and also the coil tightened onto the spark plug securely is a key factor in misfires. I've done this myself not tighten the coil fully down! Spark plugs are 22lb/ft torque I think. Well worth checking quickly and also pull out plug 8 and plug 3 and take picture and post please. 

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I look at the smoke test, i think i will try that.

I  need to dig on the leaking possibility, not easy during the week because daily car and when you start you never know when you will finish...

I will check the AOS valve too.

Spark plugs and coils, hard to believe because ii was like that before, and I replaced everything with new parts and noting changed so...

I will proceed next step by looking for leak and do a smoke test at the end of the week and hopefully i will be lucky....:)

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On 3/9/2017 at 9:50 PM, Ddavidoff said:

Following. Similar issues. I have done a lot of the same maintenance. I also found a few vacuum leaks which I fixed. 08 CTT



You might want to check out the "stutter and hesitation" thread, as it has some good info although no solution for us.


Sent from my iPhone using Tapatalk



how did you find the leak?

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