I have noticed that at freeway speeds (between 50 and 70), and in any gear, that when the engine is moving between 3,000 and 3,100 rpm that the car will surge forward despite applying no or small throttle advances. It is getting annoying as that is a common RPM range to be cruising at on the highway. It is enough of a surge that it pushes my head back if I am not anticipating it. I am running 93 octane, car is a 05 997 non-s with manual transmission.
Is there some kind of variable timing system that advances itself at that RPM? If so I think perhaps one of the solenoids that advances the system is not working as seamlessly as it should be.

 

Hmm never noticed that. Do you have the sport chrono with your non-S and is it on when you notice this?

Does it happen with cruise control on?

 

I do have the sport chorno, but both sport mode and the cruise control have been off when I noticed this. I haven't tried it with either engaged.

 

I believe that is the VarioCam kicking in. My 996 does the same thing around 3,300 to 3,400 RPM. The 997 might be set to to initiate the VarioCam at a lower RPM than the 996. Check out the link below from the Porsche web site. Once you have opened the link, click on the "VarioCam Plus" icon near the bottom of the page.

http://www.porsche.com/usa/models/91...detail/engine/

 

Possibly a combination of variocam (though at 3100 it's early) and the DME which thinks you're in crusie mode (do you drive sedately/smoothly most of the time?). Try doing some hard driving for 10 minutes changing gears at the redline and changing down 3K rpm and seeing if that has an effect. If not get the dealer to clean out your DME and start driving a little more aggressively maybe.

 

Undoubtedly Variocam, which was very noticeable on my 996, but imperceptible on my 997S. Thus, its perception either varies from car to car, or from M96 engine to M97.

-B