2003 996 stumbles a bit at cruising highway speeds

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Redman - 15 Aug 2003 07:37 GMT

I have a new (2003) 996 w/X50 option, 6-speed manual. While I am very
happy with it, at highway cruising speeds in third to fifth gears around
3,000 - 3,500 rpm, the car tends to stumble or hesitate a little when
slightly depressing the accelerator or just before releasing the
accelerator. When gently pushing in the accelerator in those gears and at
over 3,000 rpm to maintain highway speeds, the sensation is the car starts
to accelerate then seems to hesitate and surge slightly like an automatic
transmission changing gears. It does the same kind of thing when almost
releasing the accelerator. The result is that while trying to maintain a
steady highway speed, with slight changes is accelerator pressure, up or
down with stomping on it, the car seems to engage disengage engage
disengage which makes for a little jerky ride.

Assuming I am communicating this OK, is this something that can be adjusted
out? Is it weather related (i.e. heat, cold, humidity)? Also, seems a bit
worse when the A/C is running though with almost 500 hp, I don't notice any
performance deterioration when I run the A/C. If this is an idiosyncracy
of the car or any powerful manual car or something I shouldn't bitch about
in a car that mostly wants to accelerate rather than cruise along, let me
know. But if you know what to tell the Porsche tech people what to adjust
to make it cruise smoother, I would greatly appreciate you help. Thanks.

Redman

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Jim Keenan - 15 Aug 2003 14:11 GMT

> I have a new (2003) 996 w/X50 option, 6-speed manual. While I am very
> happy with it, at highway cruising speeds in third to fifth gears around
[quoted text clipped - 19 lines]
>
> Redman

We have a 2002 996. The 2002 and later normally aspirated 996 has the
3.6 liter engine with Variocam Plus, which can vary timing and valve
lift and duration. This is the same system used in the 996 Turbo.

At light throttle settings you can sometimes feel a slight surge or
"bump" from the engine, under mild acceleration, in the RPM range you
describe. This question was discussed at length in Rennlist and the
consensus was the sensation was the product of the Variocam Plus varying
settings. Virtually everyone agreed the sensation was not present (or at
least noticeable) under hard acceleration. That is the case with our car.

My guess would be you're feeling the Variocam Plus when operating in
that RPM range under light load. While the hardware is the same on the
atmospheric and turbocharged motors, the programs are different and that
may have something to do with your sensation as well. Don't be afraid to
take it in to the dealer and tell them exactly what you're feeling, but
from what we've experienced it sounds like the normal characteristic of
the engine under the narrow set of circumstances you describe.

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