Mystery bump around 3,000rpm

Anyone else experience a slight bump from the drivetrain when accelerating after a steady cruise in a tall gear? It feels like something taking up slack either in the transmission or powertrain. Always happens between 2,500 and 3,000rpm, but not consistently reproducible. New motor mount did not help, and it doesn't occur in all acceleration profiles. Ideas?

Pretty sure that's the variable valve timing engaging. I know I can feel it on my 2010 S. Thought it was clutch slip at first.

interesting question and first I've ever seen mentioned. I have a 07 CS that has done this for years with no one seemingly to acknowledge the issue or ever seems to replicate when the dealer drove it. basically said I was imagining it. I have dealt with this for many years, now have 96K on and it does not seem to be worse. I would assume there is a fix if it is a VVT issue, how hard or how much to fix this problem? thanks for any help as 'meatful', myself and others have this annoying issue......

I don't think it's an "issue," just something inherent to the way the VVT works. I know when I first asked about it a few years ago it was apparently known to be a characteristic of these cars and not something to worry about.

You can see the Dyno tune torque curve on cars that have their cars modified with headers or GT3 throttle bodies and a IDP plenum to prove their worth. Usually they will do a before modification and after in a good speed shop with up to date equipment. The curve shows a steep curve starting around 2000 rpm through 4000 then a lag until 4500/4700 then a continuation upwards. This lag is the focus of numerious modification to smooth the upwards curve. Long tube catless headers seem to be the current rage in M97 engines along with a ECU update from FVD. 9A-1 engines may use Cobb tuning to achieve this as well.

Different issue, Apex. This isn't a lag in the acceleration, it's a slight momentary "hiccup" that that you feel under light throttle going between 2500-3000.

Not sure as no Dyno tune measures light throttle hiccups

I always thought it was the dual mass flywheel as it happens on accel...but maybe its not. Either way yes my car does it 07 CS with 34k

Exactly. It feels, even under light throttle, as though something in the powertrain is taking up slack somewhere. There is a slight but noticeable bump (not a sharp bang like a busted mount). It surprises you when it happens--that is, it is not easy to reproduce consistently. It seems to happen only transitioning out of cruise in 6th gear Anyone experience this with a single mass flywheel? If there is no gear change when it happens, would a dual mass flywheel bump as power is applied? And if so, why is this not evident in lower gears or different RPMs? Could it be a gearing ratio affect (1:1 @ some RPM in 6th)?

Yup I have it too accasionally. 2007 CS w 29k mi.

6 speed MT

I know you replaced your motor mount, I too changed it to another Porsche OEM motor mount around 43k but added a Function First Orange insert to help prevent further engine movement. I am not sure I can feel or better hear any additional flat spot in the engine performance around 2500-3000 though. With a lot of modificiations to the outside of the engine that make noise, EVOMS filter and hose, GT3 throttle body, Agency Power plenum, Cargraphic headers, Miltec exhaust, I can hear small changes in the induction/exhaust systems.

I replaced the motor mount 6 months ago. Same behavior.

i'm new to porsche. had my 987.2 CS for 100 miles. the car has 76k miles on it. i too noticed this "bump". my initial thought was that it was the DMF moving about.

All three of my 987 2.7's have had it, and it put it down to the VVT kicking in. My 981 3.4 GTS had it as well, and the PDK seemed to make it more annoying. It seemed more noticeable with the more powerful engine. With the 2.7 motor, I've gotten used to it and it doesn't bother me at all.

A forum member sent me a note introducing an interesting new potential culprit: "Crank Thrust Shim. Feels like a clutch or Trans issue."

crank thrust shim-possible, but I would have expected that the wear on the shim/bearing would by now have caused other issues. I started to notice the drive train/trans taking up slack over 50K miles ago. I do regular oil changes and send the oil off to Blackstone and they are all clean......I like the VVT idea better

Yeah, we’ve all got low mileage crank thrust wear. Better all rebuild our engines! The little VVT hiccup is a known issue.

After driving the car some more, I noticed this "bump" i feel is not at 3k or any particular RPM. Rather, it's whenever I apply throttle. It really feels like the DMF or something shifting into place when throttle is applied.

That could be the engine mount, I suppose. Folks have had it wear out at 50k or so.

I have the same behavior in my 987 Spyder. Both behaviors, I should say, because they are independent. Yes, there’s a slight stumble with abrupt throttle input at lower rpm range. But even if I smoothly apply throttle 2000 rpm, and accelerate through 3000 rpm, there is a little shudder that feels like a lump in the road. Anyone riding along would think that’s what it is. Most obvious in 3rd gear, 4th is similar. I know it’s an old topic, but I think it’s worth noting that one fellow above 👆 has had 3 987’s with the exact same behavior. Must be some sort of tuning issue.

i would suggest you talk to Scott at Softronics, his ECU flash is much more robust than the Porsche maps, like 10 times more data points. which means smoother delivery of each map

I might just do that, I wish I were less sensitive to these tiny imperfections — but what kind of Porsche fan would I be — thanks for the suggestion