Rough running CTT
 

My 2008 957 CTT has been stumbling (almost like a vague misfire) for a little while and I think its getting progressively worse

I changed the coils and plugs recently as a first step (all new parts, latest version of the coils) but it didn't help

I`d swear the issue is not so noticeable when the vehicle is cold and creeps in as it warms up.

I used to just notice the smallest stumble when accelerating from low RPM (classic coils I thought hence why I changed them) but lately I also notice it when accelerating hard even in the 3000 - 4000 RPM range, no real pattern except that it`ll lose power ever so slightly for just a split second and feels like a misfire

I`ve scanned it with Durametric and there are no relevant fault codes

Any ideas? I`ve read on your tech guides that dirty injectors can cause these type of symptoms (stumbling etc) - any way to verify (check values on Durametric or something)?

I know the fuel pumps and high pressure pumps on these cars can be problematic so would these symptoms be indicative of either of these failing?

Any help would be greatly appreciated

Sniffer 500;

All the German cars are notorious for bad grounds and loops. Suggest running a 10-12ga. from the left valve cover front bolt (Furthest point) from to the drivers side inner engine

My 955 when it was purchased 2 months ago came this way and suspect it had similar problems from previous owner.

Have you changed the spark plugs? Porsche recommends the spark plugs be changed every 40k miles on a Cayenne Turbo. There is a good "How To" video on youtube that will guide you through the process. Changing the spark plugs got rid of my random misses.

https://www.youtube.com/watch?v=qoA9WFfeOR0

Can I ask what this would do? Is the issue a bad ground?

Coils and plugs were changed around 5K ago - didn't help

Its weird - I`d swear the car drives better cold and the stumbling issue creeps in as it heats up

I also believe I have a boost issue as sometimes the car surges (the boost gauge reflects what the seat of my pants feels - car initially makes 0.8 boost, then drops to 0.5/0.6 and back to 0.8 again - test conducted in 3rd gear) and others it holds a solid 0.8 boost

Yesterday, after filling up my 2009 Cayenne V6 with 92oct, I got a CEL 20min later, I checked the gas cap it is tight. When I stop at a red light it is revving/pulsing and it goes between 800 to about 1200 rpms. When I put the car in park, it started self revving/pulsing and it goes between 1000 to about 1500 rpms. Time interval between pulse is about 1-2 seconds. The next day started the car it runs perfect for 3-4 minutes but once it warms up the revving/pulsing starts again.


Brought it to the dealer - they cleared the CEL and said it was an Air Mass Sensor $858, after they brought out the car for me to leave, it started pulsing again. Now they say it is the Plugs $427. and Air-oil seperator in the intake $1,500 repair.

any thoughs ?