Engine stumble/hesitation around 2500 RPM?
 

Still breaking my engine in and taking it easy, however, I notice that when I'm in manual mode (PDK) and accelerating in 2nd (gently) the engine hesitates/stumbles around 2500 rpm but it's fine once past 3000 rpm. I don't notice it in any other gear. Is this normal? Is it the throttle bodies opening? Or is it a fueling/ECU issue?

Anyone else seen this issue?

Could possibly be the vario cam system as it switches cam profiles. My 997.2 exhibits the same symptoms and the dealer has said on numerous occasions that it's perfectly normal. Still annoying though.

Must only be you and me that have this issue!

It's strange that it's not the same in every gear. It's most noticeable in 2nd and less so in 3rd at the same revs. In 4th or higher I don't feel it at all. Doesn't make sense to me. I dread taking it the dealer to try to show them this symptom.

I've been waiting to see if anyone else has this issue... no takers though.
I think the dealer may be your only and most sensible option here.
Perhaps try to power through with a few spirited runs and see if that clears it.

Good luck.

If this persists after completing Sid's suggestion, you might try another dealer and approach it like you just started noticing it so they will evaluate with an open mind and see if they come up with anything else. The injection system has a single injection for idle and double at an increased RPM. Then it triples the injection under full load. Perhaps the 2 injection cycle is not operating properly under partial load and you're getting the triple injection under full load as engineered in the S.

ChuckJ

My 2009 Carrera had the same issue. I just took it to the dealer and they updated my PDK software which improved the transition between gear 1 and 2 and it eased up the jerkyness at low RPM. It only cost me $160 to update the PDK software. Apparently its common for the 2009 Carreras.

Since you have a 991 you may already have the most updated PDK software.

I just tested mine this morning 2013 C4S pdk) and I have no hesitation any gear at any rpm range.

I was trying it again this afternoon and unfortunately it's intermittent. Sometimes it "stumbles" and sometimes not. Only felt it in 2nd gear when hitting 2500 rpm and by 3000 rpm it's smooth sailing. Shifts are fine. Weird that I only feel it in 2nd.

Could it be MAF sensor? The dealer recently had to replace my "oil-vapor separator and vent line" and I've had this problem ever since. I believe the tech had to remove my intake,etc to do this.

What is you oil consumption like before and after the separator replacement? Did you notice a change?

ChuckJ

I haven't done enough miles to know.

One thing I've learned over the past couple of years trying to solve my assumed Variocam issues is that if your problem is not throwing codes or a CEL then the dealer is very hesitant to do any troubleshooting. After doing some online research, I found that the tech can use the PIWIS to manually actuate the Variocam system and determine if it is functioning properly. However, in order to get warranty support from Porsche, they would need to be able to justify their troubleshooting work. Long story short (in my case), no codes or CEL, no troubleshooting.

Runner is right and that's why I made my comment earlier to take it to another dealer as some dealers, like Boardwalk Porsche in Dallas, are more aggressive, industrious and persevering at finding challenging problems. Just make sure they are not biased by the knowledge that someone else has tried to fix it and failed.

BTW Attached is the torque / power curve. The car should respond relative to the RPMs shown. Note that the slope of the curve is much greater at 4000 (probably why the RPMs are allowed to spin up to near there for quick starts in a PDK equipped car).

ChuckJ

Absolutely no hesitation/stumble here. Smooth all the way regardless of if I feather the throttle or bury my foot.

Rainier

Took my car back to the dealer this morning and the tech came for a drive with me and he could also feel & hear the "stumble/hesitation". He plugged my car into his diagnostics and, of course, no faults or CEL's so I was told to drive it and see if it gets better or worse or goes away!

Techs nowadays don't seem to be able to "think" to try to figure out problems. They just rely 100% on their PC's and diagnostics and if there aren't any fault codes then everything must be fine. In reality it's not.

This was a wasted trip and the outcome was as I expected. However, my engine hestitation remains. Frustrated.

That's why I like Boardwalk in Dallas; they don't quit until it's fixed. You needed a trip to Dallas didn't you? In the meantime, you might give Cliff Blackshear (head tech) a call there to see if he's ever heard of the problem.

ChuckJ

Here's another possible cause for the stumble/hesitation (post#9) that illustrates the difficulties with no codes/cel:

https://www.6speedonline.com/forums/...ml#post2540694

Thanks, I'll give him a call. All my local dealers are the same, whether it be MB or Porsche or BMW - if it doesn't throw a code they can't or won't do anything.

Thanks, I appreciate the link and it sounds similar to my problem. I thought it could be the MAF sensor but the tech doesn't share my opinion!!

Its got to be related to the previous work that was done....

I don't know if it is or isn't but I suspect the same thing. I wish I knew for sure.

I didn't feel the stumble before the last repair because I was/am breaking the car in and was driving only in auto mode. In auto the car changes gear before the revs reach 2500 rpm under light throttle. Once I got the car back and got a few more miles on it I starting drivng in manual mode and that's when I started to feel the stumble.

I too have the stumble between 2500 and 3000 RPM on my recently delivered C2S. I remembered seeing this post and ignoring it when I saw it, but now it's happening to my car too, so I was checking to see if anyone had a solution yet.

I too have a stumble at 2500 RPM when drive the PDK in manual mode and not pressing the throttle hard. It is intermittent. Will call the local dealer for an appt.

Checked today. No stumble on the base anywhere between 2500 and 3000

So I mentioned the hesitation my C2S has between 2600 and 3000 RPM at moderate load on a Porsche survey I received, and the next day got a call from my dealer. I explained what I was noticing and although he was quite surprised I could feel it, he said that it was a "feature" of the PDK, but encouraged me to bring it in once my break-in was over. I have a feeling this is going nowhere, but I'll bring it in to give them a chance to see if they feel it too.

Has anyone else had this addressed by their dealer?

I had this when the car was brand new, under 100 miles. Though it was the Vario-cam, like others suggested

Frankly, I'd forgotten about it. Now at 700 miles, I haven't noticed it. Seems to have gone away.


As for the techs not seeming to care about solving the problem: they have no choice. The engineers at Porsche and their diagnostic systems are pretty sophisticated. A local tech, no matter how well trained, who decides to go rogue and become an artist instead of a scientist, is crossing the line. He has no incentive to do that. Doing something out of the box at this early point could actually damage your engine.

The car most likely has a noisy sensor. Since it's related to RPM, the most likely culprit is any sensor which measures the camshaft position. The tech should have a history of the most replaced sensor on the car. If the most replaced sensor is related to the camshaft, start there.

I'm experiencing it when I accelerate in 4th 5th or 6th gear between 2500-3500 rpm. Still have 400 miles to go on break in. Really haven't noticed it in 2nd or 3rd. Thought I would give this thread a bump to see if anyone had gotten an answer. More annoying than anything else, that is unless it gets progressively worse.

Still haven't taken it in. Waiting for the break-in to be over. Definitely hasn't gotten worse, but no better either.

Is this when it is warm or cold? And is it a smooth reduction of power surge or misfire?

ChuckJ

Doesn't sound like an engine misfire. Almost feels like you hit a slight bump in the road. I think it might be PDK related, but some here have felt it on their manuals also.

Definitely warm engine. Happens under gentle or aggressive acceleration. Doesn't seem like a misfire. A noticeable skip in smooth power delivery. Doesn't just skip once but a few times as you climb through that range 2500-3500.

I forgot to ask you guys if it was a 3.4 or 3.8, but my 3.4 definitely does not do that. It used to have a slight problem right after you started it and then got in that area, but I took it in for a fluids top off and they did something to fix that.

I would definitely take it in.

ChuckJ

2013 C2S here, same problem as everyone else. Stumble around 2500-2800 rpm. Happens cold and warm, most noticeable in 2nd and 3rd gear. Goes away in 4th and higher gears. Mostly just annoying. Also I have 1015 miles on the clock.

Anyone getting anywhere on this? My service dept at Jim Ellis in Atlanta won't do anything without Codes or Cel. They always say issues like this are normal and will not look into it.

Also on a side note they say the 991 electronics are not compatible with any Apple phones besides the 3GS *laugh*. I have an Iphone 5 which randomly will not present an AUX bluetooth interface. They were able to reproduce it and actually replaced the entire PCM. Issue is present on the new one as well across devices such as the Iphone 4s, 5, and android based handsets. It happens about 1 in 5 pairings and can be resolved by shutting off the car locking doors and totally restarting the PCM. I took a video of it and sent to Porsche and I am certain it is a bug.

Jim Ellis just took the "New devices" like the Iphone 4, 4s, 5 and all android handsets arent compatible yet. Really bad service on their part.

I wonder if the quality of gas has any bearing on this. I definitely notice a difference when I use anything but 93 octane Shell or Chevron gas. Now I won't use any other brand.
I haven't noticed any gear problem on my new 991 C2S pdk, now a month old.

That's a good point hockeyguy; I always use Shell 93 now and I may have started using it more consistently after I took the car in.

ChuckJ

Mine does it warm or cold. Felt mostly in 2nd and 3rd gears but I can get it to do it in any gear if I accelerate briskly from very low RPMs (not quite lugging the engine, but close). teebo, let me know if you get Ellis to address it. Mine will be going to Hennessy after I'm done breaking it in, but I can see how they might say that they can't feel the stumble.

Started happening today right around 2500rpm.
A 2012 3.8 MT with 3400 miles.
Not sure if the OP or another else found a resolution for this issue.
Thanks

So I finally took it to the dealer to see if there was a solution to this. They told me there was a software update for the PDK, so I was optimistic that that might improve things. I got the car back today, and it's as bad as before. It's really annoying and it's taking the pleasure out of my new car purchase. I can't believe more people aren't noticing this.

This is a new "development" that was certainly not there during the first 2000 miles.
Once you recognize it and become aware of it, it really does detract from the driving experience. Mtony - I feel your pain.

Perhaps more people aren't noticing it because it is so much more pronounced during casual driving and not when flooring it. Definitely a dead spot.