So I've been having a problem with my 08' 957 S. Say you're driving on the highway in 5th or 6th gear. You want to pass someone,so you give it some gas and the truck downshifts to 4th or 5th gear. During that time,the truck feels like it has a loss off power,stutters,almost like a misfire of some sort. No codes have come up,but i changed the plugs and coils anyway. Still had the problem and no codes. I take it to the dealer and they pull up a bad cat code. They will change it under warranty if it comes back after they clear the code. They clear the code,I drive it for a week and bring it back but the code does not come back. They service guys don't know what to tell me,because without a code coming up they can't tell me what it is. Anyone else having a problem like this? I talked to a local porsche tuning shop and he mentioned something about intake manifold gaskets going bad? I don't think that would cause the problem though. Any input would be great.

 

Does it feel kind of like the clutch might be slipping while boosting under hard acceleration? My turbo was doing the same thing along with hard shifts. I am changing out the valve body on the tranny to see if it is the problem.

 

Mine has done something similar to that, while getting on the highway under decent but not spirited acceleration it will have zero power delivery. Kindof like you are trying to go somewhere with the clutch pushed in. And the PSM light comes on saying DANGER DANGER. Then as soon as it shows up it goes away and never have any troubles the rest of the day. Is this what you are talking about happening?

I dont see what intake gaskets would do with the situation. If it was a turbo I could see a boost leak being an issue.

 

I had a similar problem on my 04 CS at around 210 000 km. There was a loss of power on acceleration and surging when coming off the power , kind of felt like "pulsing" , but not really picking up speed. There were no fault codes. Problem was solved by replacing the pre cat oxygen sensors (I also changed MAF sensors, spark plugs and ignitors which did not help).

 

A bad intake gasket could cause it to run lean which could cause it. I would try the simplest thing first like a clogged fuel filter. I have no idea where they are on your car or weather there is more than one.

 

Unfortunately, without codes.. this is essentially a guessing game. With that said, on a CTT you can unplug both MAFs and the vehicle will still run normally; partly due to the MAP sensor. This is an easy and free way too see if your MAFs are causing hesitation/back firing issues.

However, not sure if this will work on a NA engine since I am not sure if they have a MAP sensor as well. I suppose you can still try to unplug the MAFs and worst case scenerio, just plug them back in if you see any issues.

 

I've tried that and still had the same problem. I am going to try resetting the throttle. These cars learn your driving habits and sometimes need to be reset.

 

Does it shift hard when you put your foot down?

 

I swapped out my valve body and it fixed the surge/slipping feeling + the hard shifts.

 

Hi there, so when you say 'the hard shifts' do you mean like your driving in 5-6th gear and you want to step on it a little so i accelerate when it changes to 3-4th gear it gives out this thumping sound like hard knocking sound in the shifting? I have that problem with my Cayenne s 2004. Could that just be my sparks needing change or what could be the problem? The cpu gives out no error..

 

That's how is starts. It will eventually feel like someone ripped out your tranny.