997.2 C4S - 3200-4000 RPM Vibration / Stumble
12-28-2023, 08:24 AM
#1
3rd Gear
Thread Starter
997.2 C4S - 3200-4000 RPM Vibration / Stumble
Long time lurker from the Netherlands here - Rennlist seems to be the authority when it come to everything Porsche, so hope you guys can help!
Recently bought a 2009 997.2 C4S PDK with about 90k Miles, great car which is unfortunately suffering from a pretty intense vibration / stumble between +- 3200-4000 rpm, which almost feels like a misfire and can be felt through the entire car. Below 3200 rpm and above 4000 rpm its fine.
It's very difficult to feel in gear 1-3, from 4 onwards it becomes more and more pronounced. 6th gear seems to be the worst, in 7th you are already doing highly illegal speeds so a bit difficult to thoroughly test. It's not speed related, car is sitting on 2-year old N-rated Michelin PS2's and when you rev the engine in neutral, it's completely smooth without issues. So everything seems te be pointing to a drivetrain imbalance..?
After taking the car to a Porsche specialist the following has been inspected and done:
- No EML showing, no fault codes in PIWIS (literally zero)
- No damage to underbody - no visible damage to any drivetrain or suspension components
- PDK is shifting normally, no clunks or noises at low speed from the differentials
- Fitted new engine mounts as they were still original and sagging
- Fitted new Guibo Flex Disc as it was original and badly cracked
Both the engine mounts and the Guibo made absolutely zero difference.
Separate to the issue, the following has been recently replaced as well:
- New front Bilstein B4 PASM shock absorbers
- New battery
- New MAF sensor
- New engine air filters
Both myself and the specialist are a bit at a loss what to do next? Anyone recognise this issue or has some input where to go next?
Drive shafts? CV joints? Propshaft? (Seems unlikely as changing the Guibo made no difference?) PDK Recalibration? (seems a long shot as the transmissions is performing fine?) Change the Diff oil? Variocam Solenoids (wouldn't these through an error in PIWIS?)
Any help is much appreciated!
Recently bought a 2009 997.2 C4S PDK with about 90k Miles, great car which is unfortunately suffering from a pretty intense vibration / stumble between +- 3200-4000 rpm, which almost feels like a misfire and can be felt through the entire car. Below 3200 rpm and above 4000 rpm its fine.
It's very difficult to feel in gear 1-3, from 4 onwards it becomes more and more pronounced. 6th gear seems to be the worst, in 7th you are already doing highly illegal speeds so a bit difficult to thoroughly test. It's not speed related, car is sitting on 2-year old N-rated Michelin PS2's and when you rev the engine in neutral, it's completely smooth without issues. So everything seems te be pointing to a drivetrain imbalance..?
After taking the car to a Porsche specialist the following has been inspected and done:
- No EML showing, no fault codes in PIWIS (literally zero)
- No damage to underbody - no visible damage to any drivetrain or suspension components
- PDK is shifting normally, no clunks or noises at low speed from the differentials
- Fitted new engine mounts as they were still original and sagging
- Fitted new Guibo Flex Disc as it was original and badly cracked
Both the engine mounts and the Guibo made absolutely zero difference.
Separate to the issue, the following has been recently replaced as well:
- New front Bilstein B4 PASM shock absorbers
- New battery
- New MAF sensor
- New engine air filters
Both myself and the specialist are a bit at a loss what to do next? Anyone recognise this issue or has some input where to go next?
Drive shafts? CV joints? Propshaft? (Seems unlikely as changing the Guibo made no difference?) PDK Recalibration? (seems a long shot as the transmissions is performing fine?) Change the Diff oil? Variocam Solenoids (wouldn't these through an error in PIWIS?)
Any help is much appreciated!
12-28-2023, 04:37 PM
#2
RL Community Team
Rennlist Member
Rennlist Member
2009 C2S 194K miles
Yea, you are going to have to live with it. Same for me. As for the longer-term, it will get less... why I have no idea. I would describe the phenomenon as a super-brief, momentary cut in fuel.
Many years ago, there was a flury of cars whos owners complained about this... in short, it appears to be the variocam changeover. Notice the stumble is never exactly the same RPM so it depends what you are doing at that time. If I run it hard through the gears, I can not feel it... just sorta has to be the right conditions. Near my old home, there was a rise and with just enough throttle and load on the car... well at first I thought I hit a stick in the road.
Some have it, others don't have it. It appears to be hit or miss and mostly with 2009 cars although I have read others in other forums have complained about it. I took it to the Porsche dealer and the tech went for a ride with me ... "yep, I heard of this... yep you have it... yep, keep an eye on it" Seriously, that was that.
So.... tip: You have an S therefore you have a faky sound maker in the airbox. I found that flap opens/closes at the same time as the changeover and you can make it appear to be less by disconnecting it. By disconnecting it, you get a bit more lower-tone sound when idling so I liked disonnecting mine. On the right side of the airbox, you will see an air valve solenoid. Unplug the electrical connection (do not unplug the hoses). You won't trip a light on your dash, but you will see a code thrown with a scanner... something like ".... air flap...", Disconnecting this solenoid will help.... give it a try, you can always reconnect it without any downside at all. According to Porsche, this flap is for aesthetics only and not performance... I have the tech documentation that denotes this, so don't worry about it. I have been running with this thing disconnected for many years now. Another tip: Put in a heavier, Porsche-approved oil. I use LiquiMoly Leightlouf 5W-40 ... I don;t want to turn this into an oil thread, but you can't buy Mobil One in 5 litre jugs in this weight although they do make it. https://www.liqui-moly.com/en/us/lei...0330.html#2331 I have no proof other than my own feelings, but a heavier weight may... may... lessen the affect of the changeover. The vairocam is triggered by a solenoid valve that turns oil on/off, oil pressure moves the mechanism and it is possible that this slightly thicker oil helps the the "thunk". Porsche denotes in your manual that you can use any oil with the Porsche-specified "A40" designation.
If you want any documentation on that air flap thingy, PM me.
Some more reading and stuff:
https://www.6speedonline.com/forums/...00-rpm-48.html
https://rennlist.com/forums/997-foru...at-3k-rpm.html
(I thought it may the some air turbulance caused by the flap... could be... don't know)
Peace
Bruce in Philly (now Atlanta)
Yea, you are going to have to live with it. Same for me. As for the longer-term, it will get less... why I have no idea. I would describe the phenomenon as a super-brief, momentary cut in fuel.
Many years ago, there was a flury of cars whos owners complained about this... in short, it appears to be the variocam changeover. Notice the stumble is never exactly the same RPM so it depends what you are doing at that time. If I run it hard through the gears, I can not feel it... just sorta has to be the right conditions. Near my old home, there was a rise and with just enough throttle and load on the car... well at first I thought I hit a stick in the road.
Some have it, others don't have it. It appears to be hit or miss and mostly with 2009 cars although I have read others in other forums have complained about it. I took it to the Porsche dealer and the tech went for a ride with me ... "yep, I heard of this... yep you have it... yep, keep an eye on it" Seriously, that was that.
So.... tip: You have an S therefore you have a faky sound maker in the airbox. I found that flap opens/closes at the same time as the changeover and you can make it appear to be less by disconnecting it. By disconnecting it, you get a bit more lower-tone sound when idling so I liked disonnecting mine. On the right side of the airbox, you will see an air valve solenoid. Unplug the electrical connection (do not unplug the hoses). You won't trip a light on your dash, but you will see a code thrown with a scanner... something like ".... air flap...", Disconnecting this solenoid will help.... give it a try, you can always reconnect it without any downside at all. According to Porsche, this flap is for aesthetics only and not performance... I have the tech documentation that denotes this, so don't worry about it. I have been running with this thing disconnected for many years now. Another tip: Put in a heavier, Porsche-approved oil. I use LiquiMoly Leightlouf 5W-40 ... I don;t want to turn this into an oil thread, but you can't buy Mobil One in 5 litre jugs in this weight although they do make it. https://www.liqui-moly.com/en/us/lei...0330.html#2331 I have no proof other than my own feelings, but a heavier weight may... may... lessen the affect of the changeover. The vairocam is triggered by a solenoid valve that turns oil on/off, oil pressure moves the mechanism and it is possible that this slightly thicker oil helps the the "thunk". Porsche denotes in your manual that you can use any oil with the Porsche-specified "A40" designation.
If you want any documentation on that air flap thingy, PM me.
Some more reading and stuff:
https://www.6speedonline.com/forums/...00-rpm-48.html
https://rennlist.com/forums/997-foru...at-3k-rpm.html
Peace
Bruce in Philly (now Atlanta)
Last edited by Bruce In Philly; 12-28-2023 at 04:53 PM.
01-02-2024, 05:17 AM
#3
3rd Gear
Thread Starter
Thanks Bruce, appreciate the detailed reply and have been watching your 'journey' with interest. Based on your posts, I will also be replacing my throttle body and seal as part of preventative maintenance and hopefully some performance gains off the line.
Unfortunately I do think my issue is a bit more substantial, it doesn't do it at just one point between 3200-4000 rpm, it does it all the way between that range. It really does feel like one of the tires is not balanced, however, when you stop accelerating, the stumble stops immediately and it's speed independent.
Over the weekend I tried out the 2WD trick on the 997.2's (Sport Plus on, PSM off, handbrake up one click) and presto, RWD only on my C4S! Couldn't believe at first it actually worked, but trust me it did! Pretty cool that Porsche engineered that. It didn't change my issue though, so perhaps a pointer in the right direction, that it isn't coming somewhere from the front axle?
On another note, the previous owner did have the AOS replaced about a year ago - so I wonder whether there might be a vacuum leak somewhere if it wasn't reinstalled right? Then again, no faults in PIWIS..
My next big bet are the rear drive shafts, unfortunately all out of stock aftermarket and big bucks at Porsche (>$1200 each!) so will try to do as much diagnosis before doing so.
Unfortunately I do think my issue is a bit more substantial, it doesn't do it at just one point between 3200-4000 rpm, it does it all the way between that range. It really does feel like one of the tires is not balanced, however, when you stop accelerating, the stumble stops immediately and it's speed independent.
Over the weekend I tried out the 2WD trick on the 997.2's (Sport Plus on, PSM off, handbrake up one click) and presto, RWD only on my C4S! Couldn't believe at first it actually worked, but trust me it did! Pretty cool that Porsche engineered that. It didn't change my issue though, so perhaps a pointer in the right direction, that it isn't coming somewhere from the front axle?
On another note, the previous owner did have the AOS replaced about a year ago - so I wonder whether there might be a vacuum leak somewhere if it wasn't reinstalled right? Then again, no faults in PIWIS..
My next big bet are the rear drive shafts, unfortunately all out of stock aftermarket and big bucks at Porsche (>$1200 each!) so will try to do as much diagnosis before doing so.
