What is the current state of the 'engine stumble' issue?
09-04-2019, 12:06 AM
#301
so, today i changed the AOS ( air oil separator ).
I did this, as i suspected to be the cause for the oil pool in the passenger side intercooler hose.
This oil build up, was being pushed up the intake system, all the way to the throttle body. This means , oil on the MAP sensor. Also today i found out that the car has anothe MAP sensor on the passenger side intake. Right in the middle. i never knew it, and never cleaned it.
Anyway, i took some photos with my phone and shared them with you to see what is going on in this part.
What i did noticed is one major difference between the part from factory and the new one. On the back, the factory one has a small nipple, ( not sure how to say otherwise ), with a hole in it. Like a small breather..? you can see it clearly in the photos.
The new part, still original from Porsche, but at the third revision, has this hole covered. i assume the ditched that breather..
Out of curiosity, i opened the old AOS to understand better how it works ( failed ), and to see what is inside.
Maybe someone with better knowledge of how this system works, can explain it better for us.
To reach this part i removed the following:
- rear bumper, rear wing , wing mechanism, airbox, y -pipe ( ipd ), throttle body ( which i cleaned , as it had some deposits. Not sure if those had some influence on how the car was running, but i cleaned it off ), pelnum ( ipd ), intercooler hoses, top and bottom ones.
- i also removed the ECU or DME , to gain better access to the AOS.
After i changed the AOS, i started fitting all back toghether. I cleaned all the parts from any oil residues, and inspected very carefully every part.
I did noticed something odd on the IPD plenum. this has one small hose in the back, with one vacuum valve. it was kinda loose, and the hose was dirty with oil. I added 2 clamps to keep everything thigh and installed the ipd plenum back in it's place.
checked all the vacuum lines and everything was fine.
As i suspected bad fuel in the fuel tank, i opened that also, and drained all the fuel out. It seemed clean and with no contamination of any kind. water, or other stuff.
Put new fuel in. OMV 100.
I also re-adapted the throttle body, erased all errors, and finished up the car.
In conclusion, the car runs great now. it seems more powerful, pulls very good from low rpm, and most important, no stumble of any kind. not even from the 7th gear at 60-65km/h. drops 2-3-4 gears and goes away, depending on the throttle input.
I cant say it is really gone, until i drive it for a few more days to observe how it behaves.. but i really hope it is gone.
I cant say that i found the solution. And that replacing the AOS is the key to the problem.
But all that i did today, led to a change on how the car is running. For now at least.
I will update you if anything changes. in better or worse.
I did this, as i suspected to be the cause for the oil pool in the passenger side intercooler hose.
This oil build up, was being pushed up the intake system, all the way to the throttle body. This means , oil on the MAP sensor. Also today i found out that the car has anothe MAP sensor on the passenger side intake. Right in the middle. i never knew it, and never cleaned it.
Anyway, i took some photos with my phone and shared them with you to see what is going on in this part.
What i did noticed is one major difference between the part from factory and the new one. On the back, the factory one has a small nipple, ( not sure how to say otherwise ), with a hole in it. Like a small breather..? you can see it clearly in the photos.
The new part, still original from Porsche, but at the third revision, has this hole covered. i assume the ditched that breather..
Out of curiosity, i opened the old AOS to understand better how it works ( failed ), and to see what is inside.
Maybe someone with better knowledge of how this system works, can explain it better for us.
To reach this part i removed the following:
- rear bumper, rear wing , wing mechanism, airbox, y -pipe ( ipd ), throttle body ( which i cleaned , as it had some deposits. Not sure if those had some influence on how the car was running, but i cleaned it off ), pelnum ( ipd ), intercooler hoses, top and bottom ones.
- i also removed the ECU or DME , to gain better access to the AOS.
After i changed the AOS, i started fitting all back toghether. I cleaned all the parts from any oil residues, and inspected very carefully every part.
I did noticed something odd on the IPD plenum. this has one small hose in the back, with one vacuum valve. it was kinda loose, and the hose was dirty with oil. I added 2 clamps to keep everything thigh and installed the ipd plenum back in it's place.
checked all the vacuum lines and everything was fine.
As i suspected bad fuel in the fuel tank, i opened that also, and drained all the fuel out. It seemed clean and with no contamination of any kind. water, or other stuff.
Put new fuel in. OMV 100.
I also re-adapted the throttle body, erased all errors, and finished up the car.
In conclusion, the car runs great now. it seems more powerful, pulls very good from low rpm, and most important, no stumble of any kind. not even from the 7th gear at 60-65km/h. drops 2-3-4 gears and goes away, depending on the throttle input.
I cant say it is really gone, until i drive it for a few more days to observe how it behaves.. but i really hope it is gone.
I cant say that i found the solution. And that replacing the AOS is the key to the problem.
But all that i did today, led to a change on how the car is running. For now at least.
I will update you if anything changes. in better or worse.
09-18-2019, 08:10 PM
#302
Rennlist Member
How to determine during a test drive?
I am traveling to test drive a car I'm strongly considering purchasing. Is there a way to detect or cause it to stumble? I will have a very limited opportunity to drive the car and make a decision to buy the car. It's an out of town purchase so I have one shot.
Is there a procedure to cause it or a certain rpm range it should happen in? This is a manual transmission, if that makes any difference
Is there a procedure to cause it or a certain rpm range it should happen in? This is a manual transmission, if that makes any difference
09-19-2019, 12:12 AM
#303
Gently accelerate through 1st and 2nd. If you feel a slight stumble around 2200rpm, it's there.
It's very minimal, but if you floor it you'll never even notice it.
It's very minimal, but if you floor it you'll never even notice it.
09-19-2019, 02:39 AM
#304
I remember experiencing the stumble on my first test drive of my 997.2 GTS - it has not gone away since, but a switch to 5W50 oil helped to alleviate the symptoms to some extent.
09-19-2019, 12:01 PM
#305
for my experience (PDK turbo user here) most noticeable in 7th gear above 2000 rpm 40% throttle to accelerate on the highway.
hopefully now you have a couple different methods of diagnosing haha
hopefully now you have a couple different methods of diagnosing haha
09-20-2019, 12:30 AM
#306
Rennlist Member
Thanks for the help. I am flying down south Saturday to check out, drive, negotiate and hopefully reach a deal. The stumble issue has been in the back of my mind. I'm glad you guys stepped forward and told me what to look for. So it sounds like light acceleration in 1-3rd gears. 2200-2500 rpms. I don't think I'll be cruising enough to try in 7th. Wish me luck.
Thanks for your help.
Thanks for your help.
09-21-2019, 08:54 PM
#308
Racer
My car (14 C4S PDK) also has this slight soft spot during mild acceleration, just a slight lag, ever so slight. It doesn't really affect functionality. I suspect it is the brains trying to solve for your next input, transmission cams, atmospheric conditions, fuel efficiency factors etc. I'm not bothered...
09-21-2019, 09:18 PM
#309
Rennlist Member
Im on my 2nd 991. First was a 2015 manual C2S i traded at 10k miles. This one is a 2017 PDK C2S that i upgraded at 1400 miles with X51 PowerKit, and it now has 8200 miles. Never experienced any stumble of any sort. Never! But after starting off, i do tend to cruise near 3000 rpm in Sport and Manual Modes only.
It's a 911! It's a sportscar. Drive it like one!
Save driving in Normal and Auto modes for the non-gearheads that drive it.
It's a 911! It's a sportscar. Drive it like one!
Save driving in Normal and Auto modes for the non-gearheads that drive it.
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991.1GTS (09-21-2019)
10-23-2019, 12:28 PM
#310
Ok guys...have some news on this, i think Mufus was on to it.
When i did my plugs/coils on the car i had to pull the turbo charge pipe coming directly off the turbo and noticed on the passenger side (US car) that there was a good bit of oil that drained out. Was a little worried that the turbo was blown or on its way out but i looked it up on the forum and found some other people had experienced the same thing when removing the pipe. Also with a blown turbo you get a lot of shaft wiggle an mine was super tight. Put the car back together and went out on the highway and still had the stumble / shudder. Came back pulled the MAP sensor and noticed it was covered in oil...cleaned that...no difference...thats when i came online and found this thread haha.
So when Mufus stated he was going to change the air/oil separator he peeked my interest, getting oil all over these parts can't be good to take accurate readings, and having excess oil in a finely tuned DI motor can't be good either. So i decided to do a couple change over valves and the air oil separator valve all at once. When i got in there the whole passenger side of the charge piping and intercooler were covered in oil, cleaned the firs AND second MAP sensor, wiped out all the intercooler piping, tried to blow out the intercooler to the best of my ability and put it all back together.
Also to note the new Air/oil separator did have a revision in it. there was a breather that was blocked off now....and this breather was spewing oily air on the underside of the intake manifold.....hmmm
So i put everything back together and go out for a ride, initial throttle input seems a bit smoother (placebo effect likely) then i get it into high gear and lean on it half throttle at 2300rpm the rpm's start to climb... 2400, 2500, 2600 no stumble...super excited!! oh wait, little hesitation...yep stumble around 2900rpm.
Ok...kill me. But i know this is good preventative maintenance and the A/O separator is a revved up part so whatever.
Flash to a week and change later, and i'm about to pass someone on the highway...seventh gear...30% throttle...car scoots along, doesn't down shift, surge of turbos comes on and no stumble.....It's funny that i noticed it being smoother than usual, basically i had just been reprogrammed to accept the fishing line tug so this buttery smooth acceleration seemed off to me haha. Try it again but this time with the magnifying lens on it...very very slight stutter....again....little less....again...little more haha. Overall much better than before.
So i have been driving it for 4 weeks and it has gotten SIGNIFICANTLY better than it was before. to the point where i almost don't notice it until i really hunt for it. And i think it will continue to get better, i'm going to see if i can add an additional catch can to the passenger side charge pipes to expedite the process. I'm going to use some CRC at my next oil change and also pull the passenger side charge pipe and let what ever is in there drain out. Just to try and keep doing the house cleaning so to speak.
ALSO, i figured this wouldn't be a porsche only thing...so i looked up "DI shudder under acceleration" what do ya know...ford ecoBoost motors do the same thing, and one of the "fixes" is to literally drill a tiny hole in the intercooler end tank. This just allows the oil in the system to drain out whenever instead of recirculating it into the combustion chamber.
Ok, so some people will say...But that's just on a turbo motor; nope. the A/O separator is in the same spot on most of the newer porsche motors and would do the same thing, recirculate oil vapor until it collected enough to have some volume to get into the combustion chamber and likely produce a little hesitation. Why don't all cars do it? probably just a crappy A/O separator from the factory, or some accompaniment of parts that exacerbate the scenario. Why wouldn't porsche step up and do this? its a long job to do hours wise, it doesn't actually affect any real driving conditions in a dangerous way, and once there is oil in the system the "fix" is probably to clean the whole system which would be a nightmare. I'll keep you guys posted on the next oil change/drainage of oil on the passenger side to see if it continues to reduce the hesitation.
Hopefully this helps, any input is appreciated. and Thanks for all the help Mufus!!
When i did my plugs/coils on the car i had to pull the turbo charge pipe coming directly off the turbo and noticed on the passenger side (US car) that there was a good bit of oil that drained out. Was a little worried that the turbo was blown or on its way out but i looked it up on the forum and found some other people had experienced the same thing when removing the pipe. Also with a blown turbo you get a lot of shaft wiggle an mine was super tight. Put the car back together and went out on the highway and still had the stumble / shudder. Came back pulled the MAP sensor and noticed it was covered in oil...cleaned that...no difference...thats when i came online and found this thread haha.
So when Mufus stated he was going to change the air/oil separator he peeked my interest, getting oil all over these parts can't be good to take accurate readings, and having excess oil in a finely tuned DI motor can't be good either. So i decided to do a couple change over valves and the air oil separator valve all at once. When i got in there the whole passenger side of the charge piping and intercooler were covered in oil, cleaned the firs AND second MAP sensor, wiped out all the intercooler piping, tried to blow out the intercooler to the best of my ability and put it all back together.
Also to note the new Air/oil separator did have a revision in it. there was a breather that was blocked off now....and this breather was spewing oily air on the underside of the intake manifold.....hmmm
So i put everything back together and go out for a ride, initial throttle input seems a bit smoother (placebo effect likely) then i get it into high gear and lean on it half throttle at 2300rpm the rpm's start to climb... 2400, 2500, 2600 no stumble...super excited!! oh wait, little hesitation...yep stumble around 2900rpm.
Ok...kill me. But i know this is good preventative maintenance and the A/O separator is a revved up part so whatever.
Flash to a week and change later, and i'm about to pass someone on the highway...seventh gear...30% throttle...car scoots along, doesn't down shift, surge of turbos comes on and no stumble.....It's funny that i noticed it being smoother than usual, basically i had just been reprogrammed to accept the fishing line tug so this buttery smooth acceleration seemed off to me haha. Try it again but this time with the magnifying lens on it...very very slight stutter....again....little less....again...little more haha. Overall much better than before.
So i have been driving it for 4 weeks and it has gotten SIGNIFICANTLY better than it was before. to the point where i almost don't notice it until i really hunt for it. And i think it will continue to get better, i'm going to see if i can add an additional catch can to the passenger side charge pipes to expedite the process. I'm going to use some CRC at my next oil change and also pull the passenger side charge pipe and let what ever is in there drain out. Just to try and keep doing the house cleaning so to speak.
ALSO, i figured this wouldn't be a porsche only thing...so i looked up "DI shudder under acceleration" what do ya know...ford ecoBoost motors do the same thing, and one of the "fixes" is to literally drill a tiny hole in the intercooler end tank. This just allows the oil in the system to drain out whenever instead of recirculating it into the combustion chamber.
Ok, so some people will say...But that's just on a turbo motor; nope. the A/O separator is in the same spot on most of the newer porsche motors and would do the same thing, recirculate oil vapor until it collected enough to have some volume to get into the combustion chamber and likely produce a little hesitation. Why don't all cars do it? probably just a crappy A/O separator from the factory, or some accompaniment of parts that exacerbate the scenario. Why wouldn't porsche step up and do this? its a long job to do hours wise, it doesn't actually affect any real driving conditions in a dangerous way, and once there is oil in the system the "fix" is probably to clean the whole system which would be a nightmare. I'll keep you guys posted on the next oil change/drainage of oil on the passenger side to see if it continues to reduce the hesitation.
Hopefully this helps, any input is appreciated. and Thanks for all the help Mufus!!
The following users liked this post:
duxsi (10-24-2019)
10-23-2019, 12:41 PM
#311
Ok guys...have some news on this, i think Mufus was on to it.
When i did my plugs/coils on the car i had to pull the turbo charge pipe coming directly off the turbo and noticed on the passenger side (US car) that there was a good bit of oil that drained out. Was a little worried that the turbo was blown or on its way out but i looked it up on the forum and found some other people had experienced the same thing when removing the pipe. Also with a blown turbo you get a lot of shaft wiggle an mine was super tight. Put the car back together and went out on the highway and still had the stumble / shudder. Came back pulled the MAP sensor and noticed it was covered in oil...cleaned that...no difference...thats when i came online and found this thread haha.
So when Mufus stated he was going to change the air/oil separator he peeked my interest, getting oil all over these parts can't be good to take accurate readings, and having excess oil in a finely tuned DI motor can't be good either. So i decided to do a couple change over valves and the air oil separator valve all at once. When i got in there the whole passenger side of the charge piping and intercooler were covered in oil, cleaned the firs AND second MAP sensor, wiped out all the intercooler piping, tried to blow out the intercooler to the best of my ability and put it all back together.
Also to note the new Air/oil separator did have a revision in it. there was a breather that was blocked off now....and this breather was spewing oily air on the underside of the intake manifold.....hmmm
So i put everything back together and go out for a ride, initial throttle input seems a bit smoother (placebo effect likely) then i get it into high gear and lean on it half throttle at 2300rpm the rpm's start to climb... 2400, 2500, 2600 no stumble...super excited!! oh wait, little hesitation...yep stumble around 2900rpm.
Ok...kill me. But i know this is good preventative maintenance and the A/O separator is a revved up part so whatever.
Flash to a week and change later, and i'm about to pass someone on the highway...seventh gear...30% throttle...car scoots along, doesn't down shift, surge of turbos comes on and no stumble.....It's funny that i noticed it being smoother than usual, basically i had just been reprogrammed to accept the fishing line tug so this buttery smooth acceleration seemed off to me haha. Try it again but this time with the magnifying lens on it...very very slight stutter....again....little less....again...little more haha. Overall much better than before.
So i have been driving it for 4 weeks and it has gotten SIGNIFICANTLY better than it was before. to the point where i almost don't notice it until i really hunt for it. And i think it will continue to get better, i'm going to see if i can add an additional catch can to the passenger side charge pipes to expedite the process. I'm going to use some CRC at my next oil change and also pull the passenger side charge pipe and let what ever is in there drain out. Just to try and keep doing the house cleaning so to speak.
ALSO, i figured this wouldn't be a porsche only thing...so i looked up "DI shudder under acceleration" what do ya know...ford ecoBoost motors do the same thing, and one of the "fixes" is to literally drill a tiny hole in the intercooler end tank. This just allows the oil in the system to drain out whenever instead of recirculating it into the combustion chamber.
Ok, so some people will say...But that's just on a turbo motor; nope. the A/O separator is in the same spot on most of the newer porsche motors and would do the same thing, recirculate oil vapor until it collected enough to have some volume to get into the combustion chamber and likely produce a little hesitation. Why don't all cars do it? probably just a crappy A/O separator from the factory, or some accompaniment of parts that exacerbate the scenario. Why wouldn't porsche step up and do this? its a long job to do hours wise, it doesn't actually affect any real driving conditions in a dangerous way, and once there is oil in the system the "fix" is probably to clean the whole system which would be a nightmare. I'll keep you guys posted on the next oil change/drainage of oil on the passenger side to see if it continues to reduce the hesitation.
Hopefully this helps, any input is appreciated. and Thanks for all the help Mufus!!
When i did my plugs/coils on the car i had to pull the turbo charge pipe coming directly off the turbo and noticed on the passenger side (US car) that there was a good bit of oil that drained out. Was a little worried that the turbo was blown or on its way out but i looked it up on the forum and found some other people had experienced the same thing when removing the pipe. Also with a blown turbo you get a lot of shaft wiggle an mine was super tight. Put the car back together and went out on the highway and still had the stumble / shudder. Came back pulled the MAP sensor and noticed it was covered in oil...cleaned that...no difference...thats when i came online and found this thread haha.
So when Mufus stated he was going to change the air/oil separator he peeked my interest, getting oil all over these parts can't be good to take accurate readings, and having excess oil in a finely tuned DI motor can't be good either. So i decided to do a couple change over valves and the air oil separator valve all at once. When i got in there the whole passenger side of the charge piping and intercooler were covered in oil, cleaned the firs AND second MAP sensor, wiped out all the intercooler piping, tried to blow out the intercooler to the best of my ability and put it all back together.
Also to note the new Air/oil separator did have a revision in it. there was a breather that was blocked off now....and this breather was spewing oily air on the underside of the intake manifold.....hmmm
So i put everything back together and go out for a ride, initial throttle input seems a bit smoother (placebo effect likely) then i get it into high gear and lean on it half throttle at 2300rpm the rpm's start to climb... 2400, 2500, 2600 no stumble...super excited!! oh wait, little hesitation...yep stumble around 2900rpm.
Ok...kill me. But i know this is good preventative maintenance and the A/O separator is a revved up part so whatever.
Flash to a week and change later, and i'm about to pass someone on the highway...seventh gear...30% throttle...car scoots along, doesn't down shift, surge of turbos comes on and no stumble.....It's funny that i noticed it being smoother than usual, basically i had just been reprogrammed to accept the fishing line tug so this buttery smooth acceleration seemed off to me haha. Try it again but this time with the magnifying lens on it...very very slight stutter....again....little less....again...little more haha. Overall much better than before.
So i have been driving it for 4 weeks and it has gotten SIGNIFICANTLY better than it was before. to the point where i almost don't notice it until i really hunt for it. And i think it will continue to get better, i'm going to see if i can add an additional catch can to the passenger side charge pipes to expedite the process. I'm going to use some CRC at my next oil change and also pull the passenger side charge pipe and let what ever is in there drain out. Just to try and keep doing the house cleaning so to speak.
ALSO, i figured this wouldn't be a porsche only thing...so i looked up "DI shudder under acceleration" what do ya know...ford ecoBoost motors do the same thing, and one of the "fixes" is to literally drill a tiny hole in the intercooler end tank. This just allows the oil in the system to drain out whenever instead of recirculating it into the combustion chamber.
Ok, so some people will say...But that's just on a turbo motor; nope. the A/O separator is in the same spot on most of the newer porsche motors and would do the same thing, recirculate oil vapor until it collected enough to have some volume to get into the combustion chamber and likely produce a little hesitation. Why don't all cars do it? probably just a crappy A/O separator from the factory, or some accompaniment of parts that exacerbate the scenario. Why wouldn't porsche step up and do this? its a long job to do hours wise, it doesn't actually affect any real driving conditions in a dangerous way, and once there is oil in the system the "fix" is probably to clean the whole system which would be a nightmare. I'll keep you guys posted on the next oil change/drainage of oil on the passenger side to see if it continues to reduce the hesitation.
Hopefully this helps, any input is appreciated. and Thanks for all the help Mufus!!
and then i will check everything again, ans report about the oil build up. Hopefully is not there anymore.. or significant less. We will see.
10-23-2019, 01:40 PM
#312
Rennlist Member
Interesting thread, I'm following. 7 spd manual 991.1S
Typically do find the hesitation/stumble on 2nd and 3rd gear from 2200 rpm or so to 3000/3100 rpms when just driving the car at regular or cruising speeds.
Typically do find the hesitation/stumble on 2nd and 3rd gear from 2200 rpm or so to 3000/3100 rpms when just driving the car at regular or cruising speeds.
10-31-2019, 08:43 AM
#313
Bumping to see if anyone else has attempted this fix and seen any results
07-30-2020, 05:13 PM
#314
Three Wheelin'
I'm tempted to replace the air oil separator. How DIY-friendly is it? It appears to be mounted up past the oil filter area.
07-31-2020, 03:27 AM
#315
Instructor
