Previous 2013 991 C2S build date October 2012 drove it for 20K miles, no stumble; engine got better, faster, smoother over time.

 

I believe that's a different issue. My 997.2 had that issue big time and the 991 can get it very occasionally when the engine is cold. I have not noticed anything when the engine is over 100 degrees.

ChuckJ

 

Is this 'stumble' only happening from a stop or does it happen in the 2k - 2500 rpm range? If so that could be a different issue. I've yet to find someone who had the same issue as I. In my case, when cold/normal mode, from a stop, the rpms would drop from 800 down to 600, when moving my foot from brake to gas. On a slight incline, this would normal result in a stall. End result was a new tranny. Not once have I experienced this jerking motion, but I'm keeping alert for it.

 

Here's a few thing I found:


1. Today I received a call that my problem is fixed and my car is ready. According to the service manager, it's a problem with the "crankshaft position indicator" which may need to be shimmed in order to make proper contact. It's not a common problem - there's no service update (or whatever they call it) published, but it's not the first that Porsche higher-ups had heard of it. In other words, Porsche was aware of a problem but hasn't passed on the info to their dealers. Nice


2. Since I started turning off PSM the car takes off much better.
I wont drive with PSM on anymore.
Also, I found that you should use lower throttle input initially and then wait untill the clutch fully engages, before applying heavy throttle.
But do it before the car upshifts to 2nd or you bog and then get another delay, before it drops back to 1st. (A possible test to narrow down issues...?)


3. I've been told by a friend in Stuttgart who is a VP of Engineering with MBZ who has friends that are engineers at Porsche that almost every driveability issue that comes up these days are software/engine management update related. Not mechanical.

He also told me with some dismay that there are terrible losses in communication with service managers at dealerships. Mostly the frustration is on the German side with US dealership service techs not being educated or have enough experience with their own products. Maddening for owners who have driveability issues like this that should be simple to correct but that the procedure gets mis managed on our end.


4.

5. Here is a thought related to that- does your PSE button actually work? The vacuum valve that controls the exhaust has been known to fail. From what I know of the PSE, when it is on the valves are open at idle, closed until 3-4k and then open again. If the valves failed, they would be open the whole time, which at that low rpm would reduce torque maybe just enough to throw off the PDK, just like what is happening with the aftermarket xpipe


6. Replacing both pre-cat lambdas the issue.

As an aside, I'm rapidly starting to learn that these cars don't throw fault codes until something very major is wrong. Sensors (especially MAF/Lambdas) can be far enough away from spec to have the car running like a dog, but without throwing a code. Cursory use of the PIWIS just to look for fault codes will not find the majority of issues that can cause the cars to run less then optimally. The PIWIS is capable of reading every conceivable operating parameter in real time, but without someone who REALLY understands engines (mechanically) and the DME (in real depth) to interpret what they're seeing, most faults will never be found"

 

I had my crankshaft position indicator shimmed and it made no difference. That seems to be related to the stumble on rollout that PDK users are experiencing.

 

This is why Cliff at Plano Porsche in Dallas is so good. I've seen him go through line by line of the PIWIS to ensure each data point is appropriate.

ChuckJ

 

Too bad most of these dealers have 20 something year old techs that barely graduated Jiffy Lube school.

 

This is really interesting. I'm assuming this is a PDK. In my non-PSE PDK base I rapidly push the accelerator down to get the PDK to go to 3500. It simulates slipping the clutch to get to the torque curve RPM for a faster take-off. This happens with no hesitation or bucking and the RPM goes to 3500 and stays there until the gear wheels catch up, then it locks up as normal. I have called this technique a mini-launch control in the past. If you don't press quickly the clutch locks up quickly. That tells me there is something else going wrong with See U's car.

I talked about the injection before but I forgot to mention that PSE also has vacuum tubes hooked up to it. These have been known to become dislodged and that would take an already lean mixture to unstable. In addition any of the following may have leaking / dislodged vacuum tubes:
-air cleaner box flap
-tuning flap on S
-sound symposer
-valves for exhaust flaps on PSE equipped cars
-engine cooland shut-off valve
-heat exchanger shutoff valve
-transmission heat exchanger
-shut-off valve for ATF heat exchanger on PDK vehicles

ChuckJ

 

Confirmed and absolutely correct...

 

I am aware of 5 members of my local Porsche club who drive 991's. One is a 2012, two 2013's and two 2014's. None of these cars are having stumble issues. I also stopped by my local Porsche dealer today and spoke with the Service Manager and he told me that not a single 991 sold by his dealership has come back complaining about the stumble issues. I guess we are some of the lucky ones. Good luck to all of you who are having this issue. I hope it gets resolved soon.

 

That means nothing in my book. That's what my service manager says, too.

 

Exactly ...

You'll get better information from a random guy off the street than a service manager.

The way they talk, they'd never have any cars in expect for oil changes and brake jobs.

 

Well, if your dealer is Hennessy, it seems they forget pretty quickly. I guess I'll be taking mine back for strike two of the Lemon Law procedure next week.

 

I hate to say this: Many owners may not even recognize/feel/or know what the issue is even if they ARE experiencing it. Some are just oblivious and happy to drive a 991 and others are more 'car people'/mechanically inclined, etc...

Thanks again to all the forum members who are assisting with this issue!

 

Does anyone know if there is a way to determine the S/W version loaded on the DME via the PCM?

Thx.