What is the current state of the 'engine stumble' issue?
06-10-2019, 01:43 PM
#271
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.
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.
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.
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>
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>
06-11-2019, 08:26 AM
#272
Drifting
The mild stumble that largely went away on its own was a 991.1 S 7-spd. The used 981 was a Boxster S, 6-spd. I had a 996.2 that didn't stumble but had a noticeable and annoying surge when the variocam came in. I never understood why so many other manufacturers can make their variable cam timing unnoticeable, but Porsche, the kings of automotive engineering, cannot.
06-17-2019, 01:58 PM
#273
Rennlist Member
Is it possible the stumble is a Low Speed Pre Ignition (LSPI) event? Has anyone tried a different oil with less calcium?
https://www.oronite.com/about/news/l...-ignition.aspx
https://www.oronite.com/about/news/l...-ignition.aspx
06-17-2019, 04:15 PM
#274
cool article, definitely has some substance there. I'm coming up on an oil change and will look to try this!
A bit more info for you guys.
went surfing this past thursday, hour and 45 minute drive home no noticeable difference in the car. Brought my surf gear in the house, went to move my car and it was running on 5 cylinders...well that aint good.
But then i was thinking, perfect. this might be what was happening the whole time. Tired plug, coil pack on its way out or combination of the two. So i order 6 coil packs and 6 plugs friday morning and have them for saturday day.
Replaced them all last night/this morning. Kind of a biatch of a job, super tight up in there with the turbos. Got a coil pack boot stuck on two of them, that was the hardest part of the job haha. All the plugs looked pretty good, nothing looked a miss, but at 20,000 miles on the clock i don't expect it too.
Dialed the gap back to .026" (i'm running a 93 tune) with hopes that also could help keep things smoother.
Fired it up and took it for a ride....................Exactly the same haha. One more data point!! plugs and coil packs did not seem to help mine at all.
the search continues
A bit more info for you guys.
went surfing this past thursday, hour and 45 minute drive home no noticeable difference in the car. Brought my surf gear in the house, went to move my car and it was running on 5 cylinders...well that aint good.
But then i was thinking, perfect. this might be what was happening the whole time. Tired plug, coil pack on its way out or combination of the two. So i order 6 coil packs and 6 plugs friday morning and have them for saturday day.
Replaced them all last night/this morning. Kind of a biatch of a job, super tight up in there with the turbos. Got a coil pack boot stuck on two of them, that was the hardest part of the job haha. All the plugs looked pretty good, nothing looked a miss, but at 20,000 miles on the clock i don't expect it too.
Dialed the gap back to .026" (i'm running a 93 tune) with hopes that also could help keep things smoother.
Fired it up and took it for a ride....................Exactly the same haha. One more data point!! plugs and coil packs did not seem to help mine at all.
the search continues
06-17-2019, 05:34 PM
#275
Is it possible the stumble is a Low Speed Pre Ignition (LSPI) event? Has anyone tried a different oil with less calcium?
https://www.oronite.com/about/news/l...-ignition.aspx
https://www.oronite.com/about/news/l...-ignition.aspx
06-17-2019, 11:50 PM
#276
Three Wheelin'
Could be total placebo effect but I've run Shell gas for the last 6 tanks and the car has been very smooth with none of the stumble/hesitation that I've had in the past.
Previous gas was 10% Ethanol, whereas Shell is 0%.
Previous gas was 10% Ethanol, whereas Shell is 0%.
06-18-2019, 07:51 AM
#277
Rennlist Member
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.
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.
06-18-2019, 08:47 AM
#278
Drifting
As some one who is in the market and will soon be actively looking at cars, is it possible to detect the stumble on a short test drive? how long does it take to present itself when a car is barely warmed up from sitting on a dealer lot or how can one reproduce it while a salesman is sitting to your right? They just want to get you to take a quick ride before anything like this happens and get you to sign paperwork. A PPI would catch this I suppose but why waste the money on one and instead put it towards one that doesn't stumble.
06-18-2019, 02:03 PM
#279
Is it possible the stumble is a Low Speed Pre Ignition (LSPI) event? Has anyone tried a different oil with less calcium?
https://www.oronite.com/about/news/l...-ignition.aspx
https://www.oronite.com/about/news/l...-ignition.aspx
The LSPI situation / phenomenon is really limited to GDI Turbo engines where much higher cylinder pressures are present at high load - low rpm situations. I.E. all of these DI turbo engines that produce high amounts of torque at low rpm.
It's made even worse by the constant lugging and higher gear up-shifting of the automatic transmissions which fully exploit the low rpm torque.
Operating a gasoline engine like a diesel engine in order to reduce emissions, consumption and provide an artificially high low rpm torque curve never seemed like a great idea to me and now it really seems that with nearly a decade of implementation across the industry the drawbacks of GDI turbo engines are beginning to surface and I don't think it will stop at LSPI either.
06-18-2019, 02:15 PM
#280
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Forgive me for not reading the whole thread... but,
Has anyone with the stumble issue replaced (or had cleaned (*)) their fuel injectors?
(*) Cleaning and rebalancing the old-school magnetic pulsed injectors is a common ‘10-year maintenance’ item. I haven’t looked into it for the newest technology injectors. In the 9[98]1s they are, I think piezoelectric.
Has anyone with the stumble issue replaced (or had cleaned (*)) their fuel injectors?
(*) Cleaning and rebalancing the old-school magnetic pulsed injectors is a common ‘10-year maintenance’ item. I haven’t looked into it for the newest technology injectors. In the 9[98]1s they are, I think piezoelectric.
08-17-2019, 02:50 PM
#281
ok, so here is what is happening to me.
As stated before this happens on the TT cars too.
A little about be, so you can understand better: I run a independent service and tuning shop in Bucharest.
I have a few 991 modified, one TT one, TTS and one C2S.
The first one with problems was the C2S, who had the valve timing solenoid going bad on one bank, passenger side. Porsche service diagnosed wrong ( coil pack and spark plugs ), but with the help of this forum, i found out that the solenoid was the culprit.
Changed both of them, car runs perfectly.
Now, back to the turbos. Both of them have catless Ipe-F1 exhaust. Both of them have BMC air filter, and Forge diverter valves. Both of them have new software from Germany ( mcchip-dkr ).
Now, the TTs has extra over the TT the folowing: IPD plenum, IPD Y pipe, Wagner intercoolers. nothing else, except a different version of tune.
Both were running fine until 2 months ago. First, the TTS, has 2 bad coils, which i replaced, along with all spark plugs. Porsche SA said it is not necessary to replace all coils, as these are newer generation and you can change one by one. Said ok. while in the service, i changed also the Solenoids from the valve train to eliminate all signs of the stumble.
I addmit, until today, i did not know that this is such a big problem, and thought only the TTS had this. Like someone said before, i started doubting and blaming on the tune.
So, i took out the TTS and was working fine. after a few days, the stumble appeared. But very.. strong, i think is the word for it. Now i blamed it on bad fuel, because the car was low on fuel, and i was not sure of the quality. Also the car stopped. like, engine cut off. wont start , only after a few tries.
Somehow i managed to get to the gas station ( with range 90km, and the red warning light off ), filled her up and drove away. no problems.
Here in Europe, i use OMV 100. which is top of the line, of what is available. I filled her up and went on the highway. No problems.. 300+ km/h, no issues.
A few days later, the stumble is there, happens from 1500rpm to 3000rpm. did not noticed this too much. No check engine, no warnings, no nothing.
Getting back to the start of my story, the other car, the TT, developed the same problem. did the same: changed spark plugs, valve solenoids, to be sure, and also inspected the cilinders for bore score ( client was afraid of this ). but all is fine. The stumble is the same here too. hard, like the car hits a net that is pulling it back, and then shoots right away.
At this point, i dont know what to do.
The only things i will replace next, because this is another issue with the 991 TT and TTS, will be the AOS ( air oil separator). Both have oil in the right turbo hose, which ends up on the MAP ( Mass Air Pressure ) sensor and makes the car stumble ( but with errors and check engine light ).
So, for me , the last unchecked items will be the throttle body on both cars, and the intake valves.
If you have any other suggestions, please let me know , as i start working on the TT next week, and i'm willing to check whatever you throw at me, also to replace parts, as i can get them cheaper than the dealership and sometimes faster. So, we can experiment various theories.
One more thing, the TT has 45.000km and the TTS has 75.000km. The TTS started to have this first. Both cars are MY2014, but 2013 actual year of manufacture.
All the best..
As stated before this happens on the TT cars too.
A little about be, so you can understand better: I run a independent service and tuning shop in Bucharest.
I have a few 991 modified, one TT one, TTS and one C2S.
The first one with problems was the C2S, who had the valve timing solenoid going bad on one bank, passenger side. Porsche service diagnosed wrong ( coil pack and spark plugs ), but with the help of this forum, i found out that the solenoid was the culprit.
Changed both of them, car runs perfectly.
Now, back to the turbos. Both of them have catless Ipe-F1 exhaust. Both of them have BMC air filter, and Forge diverter valves. Both of them have new software from Germany ( mcchip-dkr ).
Now, the TTs has extra over the TT the folowing: IPD plenum, IPD Y pipe, Wagner intercoolers. nothing else, except a different version of tune.
Both were running fine until 2 months ago. First, the TTS, has 2 bad coils, which i replaced, along with all spark plugs. Porsche SA said it is not necessary to replace all coils, as these are newer generation and you can change one by one. Said ok. while in the service, i changed also the Solenoids from the valve train to eliminate all signs of the stumble.
I addmit, until today, i did not know that this is such a big problem, and thought only the TTS had this. Like someone said before, i started doubting and blaming on the tune.
So, i took out the TTS and was working fine. after a few days, the stumble appeared. But very.. strong, i think is the word for it. Now i blamed it on bad fuel, because the car was low on fuel, and i was not sure of the quality. Also the car stopped. like, engine cut off. wont start , only after a few tries.
Somehow i managed to get to the gas station ( with range 90km, and the red warning light off ), filled her up and drove away. no problems.
Here in Europe, i use OMV 100. which is top of the line, of what is available. I filled her up and went on the highway. No problems.. 300+ km/h, no issues.
A few days later, the stumble is there, happens from 1500rpm to 3000rpm. did not noticed this too much. No check engine, no warnings, no nothing.
Getting back to the start of my story, the other car, the TT, developed the same problem. did the same: changed spark plugs, valve solenoids, to be sure, and also inspected the cilinders for bore score ( client was afraid of this ). but all is fine. The stumble is the same here too. hard, like the car hits a net that is pulling it back, and then shoots right away.
At this point, i dont know what to do.
The only things i will replace next, because this is another issue with the 991 TT and TTS, will be the AOS ( air oil separator). Both have oil in the right turbo hose, which ends up on the MAP ( Mass Air Pressure ) sensor and makes the car stumble ( but with errors and check engine light ).
So, for me , the last unchecked items will be the throttle body on both cars, and the intake valves.
If you have any other suggestions, please let me know , as i start working on the TT next week, and i'm willing to check whatever you throw at me, also to replace parts, as i can get them cheaper than the dealership and sometimes faster. So, we can experiment various theories.
One more thing, the TT has 45.000km and the TTS has 75.000km. The TTS started to have this first. Both cars are MY2014, but 2013 actual year of manufacture.
All the best..
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slo_991 (06-30-2022)
08-19-2019, 12:58 PM
#282
Mufus,
Thanks for all the info. I noticed that the MAP also gets oil on it when i pulled it out just to inspect it, i cleaned it and thought it may have lessened the stumble a bit but i may have just been wishful thinking because it was definitely there the next morning. I also found the intake vent foam gaskets to be completely shot, and also the stumble happens much more at speed...could the pressure surge of intake air be causing this at lower rpm and higher speed?? i know, kind of grasping at straws. I'm going to change them and see if it helps at all. The only thing i was thinking is that there could be air that is accounted for fluttering past the intake source causing a little hunting for the right mixture.
But...If you can get parts cheaper and are willing to try a few things my biggest bet would be on the primary O2 sensors (the wideband ones) i have a sneaking suspicion that is the culprit. But i haven't wanted to drop 500$ on them without more research on this as it isn't throwing a code and i can't find anything in the data logs that i am doing on m COBB that show this as the smoking gun. Love to see if the sensor just goes out by a small percent and at lower exhaust volume and finer fuel trim levels it isn't able to meter it correctly.
thanks again!!
Dane
Thanks for all the info. I noticed that the MAP also gets oil on it when i pulled it out just to inspect it, i cleaned it and thought it may have lessened the stumble a bit but i may have just been wishful thinking because it was definitely there the next morning. I also found the intake vent foam gaskets to be completely shot, and also the stumble happens much more at speed...could the pressure surge of intake air be causing this at lower rpm and higher speed?? i know, kind of grasping at straws. I'm going to change them and see if it helps at all. The only thing i was thinking is that there could be air that is accounted for fluttering past the intake source causing a little hunting for the right mixture.
But...If you can get parts cheaper and are willing to try a few things my biggest bet would be on the primary O2 sensors (the wideband ones) i have a sneaking suspicion that is the culprit. But i haven't wanted to drop 500$ on them without more research on this as it isn't throwing a code and i can't find anything in the data logs that i am doing on m COBB that show this as the smoking gun. Love to see if the sensor just goes out by a small percent and at lower exhaust volume and finer fuel trim levels it isn't able to meter it correctly.
thanks again!!
Dane
08-19-2019, 01:29 PM
#283
Interesting to see this thread bumped. I wonder if it's PDK related.
Last edited by Sajan; 08-23-2019 at 11:30 AM.
08-19-2019, 03:01 PM
#284
Mufus,
Thanks for all the info. I noticed that the MAP also gets oil on it when i pulled it out just to inspect it, i cleaned it and thought it may have lessened the stumble a bit but i may have just been wishful thinking because it was definitely there the next morning. I also found the intake vent foam gaskets to be completely shot, and also the stumble happens much more at speed...could the pressure surge of intake air be causing this at lower rpm and higher speed?? i know, kind of grasping at straws. I'm going to change them and see if it helps at all. The only thing i was thinking is that there could be air that is accounted for fluttering past the intake source causing a little hunting for the right mixture.
- This has no impact on the car's behaviour. yes those gaskets are stupid, and they go bad fast, but they on isolate a small portion of the intake sistem. Worst case scenario would be to draw some hot air from the engine bay.. but i higly doubted that would have any significance. I will replace those on both cars too.
But...If you can get parts cheaper and are willing to try a few things my biggest bet would be on the primary O2 sensors (the wideband ones) i have a sneaking suspicion that is the culprit. But i haven't wanted to drop 500$ on them without more research on this as it isn't throwing a code and i can't find anything in the data logs that i am doing on m COBB that show this as the smoking gun. Love to see if the sensor just goes out by a small percent and at lower exhaust volume and finer fuel trim levels it isn't able to meter it correctly.
- This i did one year ago, when the the TTS was throwing O2 sensors. Changed those for nothing. I suspected it was from the tune, but then , the TT with almoste same tune, had no issue with the O2 sensors. So, i ruled those out. Now i have a pair of O2 sensors sitting around.
thanks again!!
Dane
Thanks for all the info. I noticed that the MAP also gets oil on it when i pulled it out just to inspect it, i cleaned it and thought it may have lessened the stumble a bit but i may have just been wishful thinking because it was definitely there the next morning. I also found the intake vent foam gaskets to be completely shot, and also the stumble happens much more at speed...could the pressure surge of intake air be causing this at lower rpm and higher speed?? i know, kind of grasping at straws. I'm going to change them and see if it helps at all. The only thing i was thinking is that there could be air that is accounted for fluttering past the intake source causing a little hunting for the right mixture.
- This has no impact on the car's behaviour. yes those gaskets are stupid, and they go bad fast, but they on isolate a small portion of the intake sistem. Worst case scenario would be to draw some hot air from the engine bay.. but i higly doubted that would have any significance. I will replace those on both cars too.
But...If you can get parts cheaper and are willing to try a few things my biggest bet would be on the primary O2 sensors (the wideband ones) i have a sneaking suspicion that is the culprit. But i haven't wanted to drop 500$ on them without more research on this as it isn't throwing a code and i can't find anything in the data logs that i am doing on m COBB that show this as the smoking gun. Love to see if the sensor just goes out by a small percent and at lower exhaust volume and finer fuel trim levels it isn't able to meter it correctly.
- This i did one year ago, when the the TTS was throwing O2 sensors. Changed those for nothing. I suspected it was from the tune, but then , the TT with almoste same tune, had no issue with the O2 sensors. So, i ruled those out. Now i have a pair of O2 sensors sitting around.
thanks again!!
Dane
What i will try , it will be the AOS replacement on the TT first, just to see , maybe i get rid of the oil in the passenger side turbo hose.
It is very irritating, because if you have stock intercooler hoses, and you have oil build up there, it will sweat thru the hose and eventually drip on the floor.
When i saw this, i said: Impossible, the leaking oil 911 curse has returned.
Also, i will check the throttle body, and maybe i will change it, just to see if something happens. someone mentioned it.
let me know if you have other ideas.
Also, keep in mind that i have access to porsche Spare parts programme and i can pull out schematics and part numbers accoroding to vin.
I look for the parts myself..
08-19-2019, 05:15 PM
#285
Based on feedback from a group of owners (991.1 with the stumble), I can confirm that the following actions did not resolve the issue.
1. Spark plug replacement.
2. Pre Cat O2 Sensors replacement.
3. Throttle Body replacement.
4. High Octane fuel.
I hope this saves my brethren a few $$..
1. Spark plug replacement.
2. Pre Cat O2 Sensors replacement.
3. Throttle Body replacement.
4. High Octane fuel.
I hope this saves my brethren a few $$..