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PDK Revs Fluctating

Jabbah

Member
Joined
17 May 2017
Messages
7
Whilst gently accelerating the revs are surging up and down by about 100rpm. It's most notable between 1.5K-2K rpm and in higher gears. It's like the clutch keeps slipping every second or it's thinking about disengaging to shift gear but then decides not to. I've also noticed the behaviour gently accelerating out of a bend or off a roundabout, feels like the back end is squirming in time with the rev fluctuations. It's a 2010 997TTS and still under warrantee thankfully. Here are a couple of videos showing the behaviour:

https://www.youtube.com/watch?v=nhoXhb1LHNI

https://www.youtube.com/watch?v=qCJMUYApG5c

Is this just normal behaviour for the PDK or something I should get the dealer to sort out? When I took it in to show them the tech agreed it was odd behaviour, but now I've left it with them they are saying they tried another identical car and it does the same thing so must be normal. (Or that car has the same issue!) I didn't notice the behaviour before it went in to them to have the temp sensor replaced a few weeks ago but hadn't used the car that much at that point so could have missed it.
 
I've never noticed mine doing it, and I'm a bit of a gauge watcher. Is it quite noticeable? I see your lube oil pressure is up and down like a whores draws too which would indicate a genuine rev fluctuation condition.

I'd be thinking along the lines of fueling. Has it had a remap that you're aware of?
 
Mine is an 09 C2S PDK - never seen this....

...but Im going to check tonight, Im normally not holding steady gong out of bends :?:

Certainly doesn't look "normal".
 
It's certainly quite noticable when holding a steady speed and going up a steep hill. I first noticed it a trip down to Exmouth after getting it back from the OPC for a PDK temp sensor replacement. You can feel and hear the surging, I noticed it from the engine pitch and seat of the pants first rather than seeing the rev needle fluctuate. As far as I am aware it has not been remapped and is under OPC warranty with the 111 point check done before I bought it. I've checked the firmware version of the PDK and it is on the latest for this model.

You don't seem to get this behaviour when pushing on, so only when cruising. I had wondered if it was something like virtual gearing but that should have only come in with the latest PDK on the 991.2 afaik.
 
It certainly doesn't sound terminal but I'd be pushing your OPC for answers. That would drive me crackers.

Does it 'hiccup' on tick over?
 
I've noticed this with mine in auto mode, especially when it feels like it's pulling too high a gear.

Drive mine all the time in manual now and have never noticed it since :dont know:
 
There were rather a lot of software updates for various faults with the PDK , i would suggest reporting your symptoms to OPC and then they can put a ticket into Porsche for a possible update solution .

It may also be that when the temp sensor was replaced they didnt do a calibration so the box is still in its old settings that it had with the faulty sensor.

Again different calibration routines for different faults .. Opc is best port of call on this i feel .
 
Ok, checked on the way home - nothing like this.

Surging in my mind would point to fueling or throttle position sensor...sorry can't help.
 
Sounds like a fuelling issue to me, I had something very similar on my Merc, surging on a constant throttle, almost like it was trying to change gear. I had a split intercooler hose that was causing the problem, easy fix. Maybe something similar :?: Although if it was you would probably hear the hissing noise of escaping air!
 
Interesting point on the Merc. I've only had the car a few weeks and as soon as I drove it out of the OPC I got a Transmission Emergency Run light that turned out to be a broken boost actuator rod. They fixed that and then it was ok for a week until the light came back and it was the PDK Temp Sensor that needed replacing. So cetainly could be something along those lines.

They've checked all the ECU and logs but couldn't find any errors, which doesn't mean a lot really. I wanted them to do a running log of rpm and wheel speed etc to check exactly what is happening but they seem to have to go to through PCGB Technical before they can do anything not on the list.

Anyway, hopefully PCGB tech will come back with a solution and it just requires updates or calibration.
 
Mine is normal as well, so somthing is wrong. Can you feel the surge?
 
Any warrenty work has to be athorised by Porsche .. a no fault found like they have done will not be a warrenty claim so they have already done that work for free .
 
Quick update, the OPC think they have fixed the issue with a PDK readaptation / recalibration. I will see later when I get it back as they didn't seem to be able to reproduce it before so how they know it is fixed I'm not sure. PCGB said the videos showed incorrect behaviour so at least I know it is unusual. They have also given me the next (major) service for free in way of apology for 3 issues in the 8 weeks since I bought it which I'm quite happy with. Hopefully that will be it now.
 
Got the car back a couple of weeks ago and even on the drive home it was obvious that nothing was fixed. Went for a long drive this weekend and it is probably worse than it was before. Either that or I am getting better at provoking it. They are going to take it back in at some point so I will have to make sure I take one of their techs out and demonstrate the issue and then get them to recreate it whilst I am in the car.

Something else I've noticed is that in manual mode if you're cruising with say 5% throttle and then quickly go to say 15% throttle the revs will jump up ~150rpm and then go back 100rpm and then increase normally as the car accelerates. After doing that it makes it even more likely to do the fluctuating rpm behaviour. Also oil needs to be fully up to temp, when cold it is much more difficult to provoke.
 
Sounds like a change of OPC may be in order.
 

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