cclcal

wasn't sure what this thread was about until the past few weeks. feels like the transmission is just slipping and not engaging...although it was not every time. I usu experience it within the first 5 minutes of starting the car.
im @ 15k miles

so im in san diego, did you guys bring car to dealer for inspection or indy shop? do you all have a recommendation?

seems like dealers are not admitting to an issue w the car so I don't want to waste my time there.

thanks!

aCayenneFan

It is more about establishing a record of the issue presenting itself. If there is a remedy (that is less than a recall) after your warranty lapses, you will be in a better position than if you hadn't reported the issue.

Nin Din Din

minthral

981 had stumble/hesitation. It was mainly from a dead stop and a 3.5-4k range. Dealer claimed it was normal...arguing with them was lost cause...and I couldn't get any mod to fix it. Headers probably reduced it the most. Cobb tune exaggerated it even more, though I never tried their PDK tune. I tried other cars even 911s during same generation and they all did it. It was hard for me to understand by more people wouldn't complain and raise awareness for a fix... apparently either not all cars have it or some don't notice.

Sad to say, but I'd consider it just the character of the 'NA" engine. It feels like something is wrong, but apparently its just how it works. I always thought it is transmission related because it feels like a clutch slipping. Best answer I got was its intentionally tuned like that... it has to do with tranny and engine mating and launching the car, where the DME adjust things on the fly, apparently have to slip the clutch to get things working 'normally'...perhaps to reduce emissions or prolong engine life...who knows and Porsche wont even admit its a problem. Some have worse than others, but I've never seen a car that doesn't do this.

No hesitation/lag in a 991.2 and its smoother. The irony is the NA is supposed to be lag free and turbos have lag.

cclcal

car is out of warranty. wonder how much it will cost for dealer to check it out and reset PDK

Porsche of San Diego vs Carlsbad? any preferences?

TooTurbos

So after many weeks of reading researching and anguishing over this i decided that i didn't think it was a "991 turbo" issue and looked on the regular 991 forum. And here i am..... I had found a couple other small incidents where people had the shudder/jutter/fish on feeling in the turbo discussion but no real solutions


just a little background on myself. Built a couple turbo cars (yo mommas honda, and a 240sx with a 2jz), was a motorcycle mechanic, did heads/cam on my Z06, had a gen 5 viper and now have the 991 turbo. Mech Engineer and super hands on with most things haha. So this problem really really really bothers me, and i'm dedicated to smoothing it out. Absolutely love this car and want it to be as perfect as it can be, especially when you can feel how well it performs when everything is working in concert.


The reason i initially discovered my issue was after the COBB tune i installed. I unknowingly loaded on the ABR map, and at first i think it may have masked the problem because it almost forces you to drive more "on" throttle than "off". I put the tune on my car 3 days after receiving it, so i didn't have a great baseline for all the feelz of the car. I noticed it first when commuting to work and i lightly accelerated in 7th gear at around 65 mph, under 2000 rpm....shudder, shudder, and then zoom shes off... hmmmm that was weird... immediately blame i on the tune.

so then i spend the next couple days playing with the tune with Sam @ by design (super great and helpful guy). he gives me a less aggressive boost response curve and it noticeably calms down the touchiness of the throttle, but the stuttering remains. Naturally i'm thinking O2 sensor, plugs, coil, not so much gas...i find that people love to blame gas. But i tried the gas route anyway...no luck. didnt matter if i got **** gas or shell premium (i live in Boston 93 oct is everywhere). I've felt knock, boost spike/boost cut and other funky things in other cars but this felt like spark to me. Very uneasy feeling for me in car over 100k haha.

So i uninstall the COBB totally....still there, but now much less prominent because of the lowered boost levels. Now that i'm hunting for it i start to wonder if i bought an abused car, or a lemon. Now i'm getting desperate, can't find much of anything on the turbo forum. So i schedule an appointment with the dealer to just go through the car to see if everything looks in good order. Service guy says.."yea sometimes the turbos just seem to run better under more throttle, i think the fact they are trying to get the car so responsive makes it a bit jittery and under certain load conditions the boost is coming on and the car is trying to balance between spooling and normal moderate acceleration". to me this made a lot of sense, and that under certain conditions it could be tricky to dial out with the VTG and a nice breathing 3.8l motor. That, plus an additional amount of boost would exacerbate this, right? nah...everyone who tuned their cars would be bitching about this.

Then i find you guys with your problem above 2000 rpm, i'm thinking...hmmmm maybe its just the gearing? then i hear an audio file....very very different from my subtle problem.

Then i find someone describe their problem as a bass tugging on a fishing line...sounds like my problem exactly.

So i try the technique advised by one person to not allow the car to do its natural warm up cycle. start the car in the AM and make the throttle jump to 2500rpm for 5-10 seconds and then it will fall to the normal 850 rpm idle and youre fixed!!! ....seems like total voodoo to me...

and whatdya know....the friggin thing smooths out 90%; still there but barely detectable... and i'm looking for it so much i need like perfect highway. Now i'm thinking throttle position sensor or even butterfly valve motor in the throttle body or IAC valve. WHICH MAY possibly explain why someone who changed their plenum had luck. just futzing around with it/cleaning it may have jarred/jogged it and it decided to work. still just a hypothesis.

Anyway i figured i would post this because i will be purchasing a durametric system and trying to log some stuff and see what trends start to pop up between ignition timing, throttle position, O2 reading, and knock.

but to recap:

i believe there are two different problems that may be making it difficult for us to even communicate about them eloquently.

1. I believe there is some light off throttle under 3000 rpm that is to do with sensors/electronics that produces this light hesitation feeling (fish on the line really hits this on the head for my problem)
2. The much larger big hesitation that happens above the 2000 rpm mark that i heard in the audio fill that sound like fuel cut almost. much more aggressive and harsh.

I still think the upstream O2 sensor could be some of the issues, it is a wideband sensor and the computer is using it for all kinds of things. And maybe on the reset of the computer while its still "learning", the sensor isn't being used in its full spectrum. then once its settled in the edge of the sensor may just be enough to mess something up but not enough to throw a code. again just spit balling ideas around

They could totally both be related to tps or the throttle position servo, the motors in these cars are so crisp that if you go out and drive your car and kinda twitch your foot on the accelerator you can definitely get a similar feel.

Stay tuned. This has my attention haha. When i was on the Z06 forums there was a valve guide problem....i ended up doing a ton of work on that as well, these things can be solved. we just have to get some collective data and plow through it. Seems like Porsche isn't going to, and i'm not letting this incredible machine go that easily

Dane

one-rennlist

Dane, will be most interested in your telemetry of the stumble... My theory is Porsche has its own defeat device due to emission regulations. Interestingly the stumble with my 997.2 GTS is more pronounced when driving with the sport exhaust activated.

TooTurbos

Not sure i follow one-rennlist, could you expand??

I guess given the infrequency of this issue as a whole, but the fact it spans different models and years i thought it could definitely be one part/manufacturing error that could be localized?

aCayenneFan

If the stumble is more pronounced with sport exhaust activated, that would argue against the root cause being based on emission management. Sport exhaust involves opening an exhaust valve located past the catalytic converter (e.g. cat-back). If the stumble occurred say, when sport mode on the engine/transmission was triggered, that could be from an emission management function.

minthral

Hate to say it, but honestly the best fix is not to buy a car impacted (from my understanding/testing, its all of them). Many will end up buying due to lack of testing or might be blindsided. If you’re in that camp, you have to learn to live with it (AKA don’t wide open throttle at low RPMs and 1st gear) or should trade in. Later gen cars (not NA) don’t do it and are faster, but they sound worse and far more expensive. You weigh the pros/cons yourself.

My 2 cents is its variable cam timing (better known as Honda VTECH) slow to kick in likely dealing with emissions regulations and tuning. It’s important to note that despite the felt delay, the cars meet or exceed published 0-60 times. It just leaves you wanting more since its a perceptional lag and that’s the problem.

one-rennlist

The issue is reproducible in specific cars known to have it. It is interesting to see that even though not all people experience the stumble, this thread attracts owners with the same issue regularly... And now that the 991.2 and 992 are out, which have massively redesigned engines and do not have the issue, the culprit must be somewhere in the 997 - 991 NA 3.8 liter engine design.

one-rennlist

Well, I do not believe the sport exhaust being the trigger, but I suppose with the slightly reduced back pressure the engine can fluctuate its RPM more easily, hence the increased feel. The reason for my theory is that people report no stumble when fully depressing the gas pedal right after the engine startup (thus switching to a different engine management state emissions tests would not reach). The other theory I have is that there is a transition between two mappings in variable valve timing at 2000 RPM causing the stumble.

2000se

Maybe it's been answered already, but do the cars w/ tunes experience this? I also tend to agree it has something to do w/ the var valve timing.

subshooter

I have the stumble in my 981 engine (also a 9A1). It is frustrating and annoying. I also have a 991.2 (9A2) and the stumble is not there.

MJBird993

Well, I bought my 991 new (ordered it) and the issue didn't become apparent until after a few miles, although in that car it got better all by itself. My 981 was bought used, but I had it delivered and didn't recognize the problem until after I had received it. That car went in for official Porsche technician diagnosis, and the shop manager said "they all do that" so I was, as you can imagine, discouraged. So you can't always just "not buy a car impacted", unfortunately.

I should add this whole experience has really rather turned me off of Porsche, and I've not seriously considered replacing the 981 with another, and instead bought a BMW M car. BMW, as well all know, never have issues. <cough>