What is the current state of the 'engine stumble' issue?
08-17-2020, 07:11 PM
#331
Burning Brakes
Looks like Rennlist member @rnl had his variocam solenoids replaced and it solved his stumble issue. Not sure if his stumble is what we've been experiencing, but it's an easy enough DIY (if you can replace plugs/coils you can replace these two solenoids) and only $270 in parts.
I've been suspecting throttle body/sensor or variocam solenoids are the issue, but leaning towards throttle body based on how the car is acting (stuttering like it's a fuel/air issue) and that the car behaves perfectly fine for about 50-100 miles when you reset the throttle sensor (key in "accessories on" for 60 seconds, then car off, then start car). Also @Dewinator reported success with a throttle body replacement. I know a few have reported that doesn't work, but reading through all the posts all I could definitely see on the "doesn't work" was they replaced the sensor, not the necessarily the entire throttle body and sensor (you can order them separately or already integrated/connected together). I was about ready to pull the trigger on a new throttle body (with throttle body position sensor/actuator included) since it's only a $170 part if you buy the OE Bosch part (0280750473) versus the exact same part with a Porsche logo stamped on it (99760511601 or 99760511600) for $386 (on sale through Sunset). Porsche/Bosch updated the part for a reason, and maybe this was it. I figured if that wasn't the issue I'd only be out $170.
Now I'm on the fence on which way to proceed. I'm not usually the type to just throw parts at a problem, but based on this thread it would take some pretty serious equipment to properly diagnose/troubleshoot during test drives and the dealers couldn't care less. I think I'm going to do the throttle body first, and actually film the old one at different rpms to see if I can see a fluttering of the valve at the different RPMs we seem to experience the stumble (Dewinator reported his mechanic could see the valve not holding a steady position). If that doesn't solve the problem then I'll try changing out the variocam solenoids.
I've been suspecting throttle body/sensor or variocam solenoids are the issue, but leaning towards throttle body based on how the car is acting (stuttering like it's a fuel/air issue) and that the car behaves perfectly fine for about 50-100 miles when you reset the throttle sensor (key in "accessories on" for 60 seconds, then car off, then start car). Also @Dewinator reported success with a throttle body replacement. I know a few have reported that doesn't work, but reading through all the posts all I could definitely see on the "doesn't work" was they replaced the sensor, not the necessarily the entire throttle body and sensor (you can order them separately or already integrated/connected together). I was about ready to pull the trigger on a new throttle body (with throttle body position sensor/actuator included) since it's only a $170 part if you buy the OE Bosch part (0280750473) versus the exact same part with a Porsche logo stamped on it (99760511601 or 99760511600) for $386 (on sale through Sunset). Porsche/Bosch updated the part for a reason, and maybe this was it. I figured if that wasn't the issue I'd only be out $170.
Now I'm on the fence on which way to proceed. I'm not usually the type to just throw parts at a problem, but based on this thread it would take some pretty serious equipment to properly diagnose/troubleshoot during test drives and the dealers couldn't care less. I think I'm going to do the throttle body first, and actually film the old one at different rpms to see if I can see a fluttering of the valve at the different RPMs we seem to experience the stumble (Dewinator reported his mechanic could see the valve not holding a steady position). If that doesn't solve the problem then I'll try changing out the variocam solenoids.
This was a very low speed stumble...from stop.
08-17-2020, 11:02 PM
#332
Originally Posted by rnl
This was a very low speed stumble...from stop.
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Class5Kayaker (08-18-2020)
10-10-2020, 01:28 PM
#334
Three Wheelin'
Any new thoughts on this? Ever since I've gotten in the habit of resetting the throttle before most drives, the car behaves so beautifully perfect. No stumble, no hesitation, perfect downshifts. Does it stand to reason the issue might be related to the throttle position sensor, or perhaps that this is even just a software issue and not something mechanical?
10-10-2020, 11:29 PM
#335
I’m sure if there were a single cause, it would have been discovered by now. The software that adjusts the throttle position based on airflow detected is probably written in such a way that any mechanical abnormality tends to introduce oscillations.
10-11-2020, 03:18 PM
#336
Rennlist Member
09-26-2021, 02:53 PM
#337
Looks like the mecanic or somemone of us Who will find this problem will win the mecanic Nobel this year!
On my side i changed 2 of 4 variocam solenoid and did no change finally..
I got some throttle (not stable) issue...
Dont know what to do..
On my side i changed 2 of 4 variocam solenoid and did no change finally..
I got some throttle (not stable) issue...
Dont know what to do..
09-26-2021, 04:52 PM
#338
the throttle stumbles when the oil is cold. after it reaches 80-90 degrees celsius, car works fine. Switching the car on sport mode, changes the things, and stumble is gone. no hesitation no nothing.
The chains from the timing started rattling at startup. when oil is hot. when the engine is cold, no rattling. . changing the timing requires splitting the engine block in two. you can live with it. I changed the hidraulic tensioners, which made a difference for 1000km. after that, rattling is back.
one major issue, which i have no ideea if anybody had it before, is that, for an unknown reason, the wires from the MAP sensor before the throttle body, corrode down the line, in the bunch of wire from the the main engine harness.
this results in the engine stopping. randomly, jerking hard and evnetually stop. sometimes you cannot restart it. you have to leave it. after you leave it, it may start again, only to die immediately you press the gas pedal.
There are two solutions to this. first, replace the whole superior engine harness. this requires to remove the engine and intake manifold as the wires are loomed between the manfiold.
the second one which Porsche techs did to my car was to double the wires from the MAP, directly into the ecu socket. not sure if the big socket or the small one. i can check if anyone is interested.
Since this repair was done, the car work normally, and i had no issues. But two of my friends did. same thing. same repair.
Car work normal. all of them are 2014.
so i cant tell for sure why, but something happens in the wire loom, that affects these 3 wires from the MAP sensor.
i am curious if anybody had this problem.
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Miatavi (08-02-2023)
09-26-2021, 06:09 PM
#339
Interesting.
I had the Map sensor changed.. The reading when the car was off was not stable as it should do.. But no change.
The wire was not change thow.
On my side, idle is always rough Warm or cold sport or not.. https://photos.app.goo.gl/Mdz8dt19UABmbdLG6
Stumble are present at any gears.. It is like i hitted the brake when they occure.. If i let the gaz off, nothing happen but if i put a little load Just to Keep my speed... Ho it is very anoying!
What can cause car to behave like it is missing or brake are applied?? No code no nothing..
I had the Map sensor changed.. The reading when the car was off was not stable as it should do.. But no change.
The wire was not change thow.
On my side, idle is always rough Warm or cold sport or not.. https://photos.app.goo.gl/Mdz8dt19UABmbdLG6
Stumble are present at any gears.. It is like i hitted the brake when they occure.. If i let the gaz off, nothing happen but if i put a little load Just to Keep my speed... Ho it is very anoying!
What can cause car to behave like it is missing or brake are applied?? No code no nothing..
09-27-2021, 04:15 AM
#340
Interesting.
I had the Map sensor changed.. The reading when the car was off was not stable as it should do.. But no change.
The wire was not change thow.
On my side, idle is always rough Warm or cold sport or not.. https://photos.app.goo.gl/Mdz8dt19UABmbdLG6
Stumble are present at any gears.. It is like i hitted the brake when they occure.. If i let the gaz off, nothing happen but if i put a little load Just to Keep my speed... Ho it is very anoying!
What can cause car to behave like it is missing or brake are applied?? No code no nothing..
I had the Map sensor changed.. The reading when the car was off was not stable as it should do.. But no change.
The wire was not change thow.
On my side, idle is always rough Warm or cold sport or not.. https://photos.app.goo.gl/Mdz8dt19UABmbdLG6
Stumble are present at any gears.. It is like i hitted the brake when they occure.. If i let the gaz off, nothing happen but if i put a little load Just to Keep my speed... Ho it is very anoying!
What can cause car to behave like it is missing or brake are applied?? No code no nothing..
Also, i forgot to mention. the wire from the MAP issue happened on 991 Turbo and Turbo S. not Carreras. so, maybe it is a Turbo issue.
09-27-2021, 09:00 AM
#341
What i learned over the years is that 991's show as accurate as possible the RPM. in other , normal cars, they program the tachometer to stay steady at a certain rpm, while in reality, the engine fluctuates. Porsche decided to make it as accurate as possible, so this is why you see the needle moving. i never seen any 991 that has a steady RPM reading.
Also, i forgot to mention. the wire from the MAP issue happened on 991 Turbo and Turbo S. not Carreras. so, maybe it is a Turbo issue.
09-27-2021, 10:44 AM
#342
Idk if it’s related to anyones issues but anyone ever take a look at the intake valves for any Direct Injection carbon buildup
09-28-2021, 08:19 AM
#343
09-28-2021, 08:57 AM
#344
Nordschleife Master
I was hoping solenoid change was the answer. Maybe it is for some. Anyone else change solenoid and noticed a change?
09-28-2021, 12:30 PM
#345
Three Wheelin'
I'm going to replace the throttle position sensor this winter and see what happens. It's still my leading theory on my own car just based on the throttle reset procedure temporarily helping. To reset the throttle position sensor, turn the key in the ignition all the way to the on position (don't start the car), leave it there for 30+ seconds, and then proceed to start the car.
Most of my stumble/driveability issues are now isolated to when the car is cold. Once it's warm, it runs great.
All I know is there is nothing worse than having constant throttle applied and then the car jerks around as if you're riding the clutch from a standstill.
If the throttle position sensor doesn't help, my next step is going to be replacing the variocam solenoids and probably the coil packs while I'm there since they're still the originals as far as I can tell.
Most of my stumble/driveability issues are now isolated to when the car is cold. Once it's warm, it runs great.
All I know is there is nothing worse than having constant throttle applied and then the car jerks around as if you're riding the clutch from a standstill.
If the throttle position sensor doesn't help, my next step is going to be replacing the variocam solenoids and probably the coil packs while I'm there since they're still the originals as far as I can tell.