I had a "the stumble" 2 times over the course of 2 years of ownership.
In my observation I guess with me it was the following scenario:
I'm cruising along, slowly, at ease, in normal mode, in a tight bend, 2nd gear. Exiting I'm very slowly and lazily applying throttle, then for some reason my brain activates my mental sport mode, so I push the throttle hard just at the point the computer wanted to shift to 3rd gear because it noticed I was just pootling around. Just when it wanted to shift to 3rd it notices my more aggressive throttle input, which throws it off because then it has to decide to stick with 2nd resulting in a lag, hesitation, stumble.
I don't know if it is THAT stumble you guys are experiencing, but that's what I think, what I felt, happened to me two times.

 

My car is a manual, so it's not related to me trying to out-think PDK.

Let's say I'm accelerating from a stoplight. I'm not trying to drive quickly - just normal commuting kind of traffic. First gear, accelerate up to 3K RPM, shift to 2nd which puts me down at 2K RPM. Accelerate up to 3K RPM. In that acceleration in 2nd gear, I get stumbling in the 2-3K RPM range as I accelerate. It happens in all gears, but it's most noticeable in 2nd and 3rd gear with the load on the engine. Worse going up an incline. Also noticeable not on acceleration but trying to maintain 2300-2500 RPM at a constant speed - then I get the "fish tugging at your line" hesitation that has been talked about.

I'm liking this theory about fuel delivery. From the very beginning, not knowing much, it just felt to me like a fuel issue.

 

So, I am in the local dealer today waiting for my car to come out of service. I was talking to my salesman as I have a 2015 on order. He excuses himself to talk to another service customer whom he just sold a new C2s. He came back somewhat upset. I asked him if everything was okay. He explained that a customer was experiencing a problem with his three week old car. I said, I hope it was nothing serious. He said, no, the customer just is afraid to drive the car. He explained the complaint to me. I concluded the he has the "stumble". The salesman looked at me like I was nuts. I pointed him to this thread & he turned very pale. This issue clearly has not been resolved. I have a 2015 on order & hope my luck holds as I don't have the issue with my 2014 (10k). I am hoping that I stay in the 70% group. Frank C.

 

It's a lottery.

The mystery continues.

 

Porsche Cars NA knows there is an issue, but they have decided to ignore their customers, avoid the expense of fixing the issue (this engine will be extinct soon), or they really have no clue how to fix this issue. No matter what the circumstance, their response has been very disappointing.

 

I'm finally abandoning all hope of a dealer solution and will now be reaching out to independent mechanics. I've asked the president of my local PCA chapter to hook me up with a few folks who know the newer 991 engines. We'll see.

I refuse to continue disliking driving my car because of this. I will find a solution, if nothing else now just to spite PCNA who continues to ignore the issue.

 

Sadly, that's most likely your (our) best option, as I'm convinced PCNA has put out orders not to address this problem. I've got to believe someone out there can get to the bottom of this with a little bit of effort and desire. The problem is not unsolvable, it's simply that no one (PCNA) has been willing to make any effort to troubleshoot.

 

Frank, it is hard for me to believe that you are taking this risk while in possession of a mechanically sound 2014. Do not underestimate the stumble issue; it will frustrate you to no end if you end up having it in the 2015.

You are a gambler my friend. Best of luck.

Moises.

 

Stealthboy, if you go the independent mechanic route, ask them their opinion about the possibility of the lambda sensors (O2 sensors) being responsible for the stumble issue.

A while back, a fellow from England or Ireland reported solving the problem after a 20 year veteran Porsche mechanic took upon himself to solve the stumble of his car. The apparent culprit were the lambda sensors. I tried to contact th fellow several times but he never replied to my messages.

 

You have a 2015 on order? The 2016 cars are already at the dealers. I wouldn't worry too much about the "stumble." I don't have it in my 2015 GTS, and none of my friends with 991's have it.

 

If it's just the O2 sensors, those would be pretty easy to replace myself. I'll start looking into that now. Can't hurt.

 

The last build month for the 991.1 is 11/15 & all 991's are sparsely allocated. My car is in production as of last week & I expect delivery around the third week of November.

reportClicked:

 

I am throwing the dice to be sure. I believe that I can weed out any "from new" stumble issue on the delivery day with a test drive. This should lower my risk to about 15%.

reportClicked:

 

I know, but the 2016 991.1 is already in production. My dealer has some. You sure you are getting a 2015?

 

Sorry for the confusion, I ordered a 2016 not 2015.