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-   -   Engine stumble/hesitation around 2500 RPM? (https://www.6speedonline.com/forums/991/300360-engine-stumble-hesitation-around-2500-rpm.html)

991s 02-15-2013 06:22 PM

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?

runner1021 02-15-2013 08:18 PM


Originally Posted by 991s (Post 3770237)
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.

991s 02-16-2013 09:07 AM

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.

Psycho Sid 02-16-2013 09:17 AM


Originally Posted by 991s (Post 3770572)
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.

ChuckJ 02-16-2013 12:47 PM

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

firstmovado2013 02-16-2013 12:56 PM

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.

firstmovado2013 02-16-2013 12:57 PM

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

Schunmd 02-16-2013 01:03 PM

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

991s 02-16-2013 02:44 PM

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.

ChuckJ 02-16-2013 07:27 PM


Originally Posted by 991s (Post 3770797)
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

991s 02-16-2013 07:48 PM


Originally Posted by ChuckJ (Post 3770951)
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.

runner1021 02-16-2013 08:22 PM

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.

ChuckJ 02-17-2013 06:33 AM

2 Attachment(s)

Originally Posted by runner1021 (Post 3770981)
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

Rainier 02-18-2013 05:06 AM

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

Rainier

991s 02-18-2013 11:01 AM

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.


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