Mechanic

See also: http://www.planet-9.com/981-cayman-a...ommon-not.html

stealthboy

Seems to be talking about the 3K stumble which is the VarioCam transition. This is different than the 2500 stumble. Yes, it's frustrating - there are different stumbles we're experiencing.

One is a hiccup right at 3000 RPM when accelerating through that point - it's where the VarioCam changes position. But the other is felt when trying to maintain a constant velocity or accelerate slowly near the 2300-2500 RPM range.

I have both so I know they feel completely different.

eddieb4

Are these stumbles only with pdk?

stealthboy

No.

991carreradriver

The GT4 uses the 3.8 NA, which is the 991.1 S engine. Panorama (July 2016 issue, p.47) did a GT4 v. GTS review, in which I read the following: "The only fly in the ointment is an annoying stumble in the mid-range, which was persistent but somewhat intermittent. In this era of ultra-precise engine management technology, we can only conclude that such an obvious imperfection must somehow be intentional and/or an unavoidable by product of EPA compliance"

Maybe this is why the problem has never been solved. Where is a VW programmer when you need one?

Dewinator

I still feel like I got the 2500 stumble regularly prior to throttle body replacement and almost never after. Has anyone that's had the TB replaced (stock or aftermarket) had the stumble continue?

n2cars

I know this engine stumble is a mystery. Some cars have it and some not. Could this stumble have anything to do with how the engine was broken in? The reason I ask is that my wife's car does not have the stumble. The car is a 2016 C2 manual. She broke the car in literally by the book. The revs never went over 4K for the first 2000 miles. Is there any correlation here?

fastdiablo

I also followed the guidance pretty much to the letter, but I have no stumble.

Selo

I have a GT4 and I broke it in by the book, and I've never noticed a stumble. Now I'm worried to drive it again.......

96redLT4

I just read the article and this sounds like exactly what our RL members are talking about.
J

96redLT4

Interesting thought but hard to imagine how it could be break-in related.
J

pfan

"we can only conclude that such an obvious imperfection must somehow be intentional and/or an unavoidable by product of EPA compliance."

If that were the case, one would assume the defect would affect all 991 owners, not just those of us that drew the short straw.

991carreradriver

I think that all these engines have some of the stumble in the mid-range, its just some are more pronounced than others. I have had two 991's without what I would call the "stumble". I never drive in automatic mode, so I am naturally revving higher and less likely to get the lugging or stumble. Truthfully, this problem has been beat to death.
The point of my post was to let the participants (especially those with the problem) know that a national, well respected periodical recognize that it exists.

squid42

What the magazine is saying that the gt4 might have been "sabotaged" to not take away from the more expensive Porsches. They didn't know the more expensive ones have it, too.

Curvfun

My break-in period was "by the book" as well. Mine stumbles and shakes between 2 & 3K RPM's whether hot or cold. Below 2K and above 3K, it runs beautifully. If it's driven assertively through this range, the problem is of no consequence. But gradually going through this range in a neighborhood or city street causes a significant awareness of some sort of engine anomaly. The bumping and shuttering never goes away and affects the away I have to drive it just for a smooth acceleration experience. It's very disheartening, especially since some of you indicate you have no problem at all.

Wonder if the 991.2 has these issues resolved......