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How do I start to diagnose engine hesitation in a new 991?

  • 2013
  • 911 Carrera
13 000

Hello tech experts!

I have an annoying issue with my 2013 911 that has been bothering me for two years.  There is a series of stumble and hesitation in the engine when in the RPM range of 2000 to 3000.  There are several ways these manifest themselves.  One is just trying to maintain a constant velocity at say 2300 RPM.  I can feel a slight tugging sensation like the engine is being held back randomly (water in the fuel kind of feeling).  Another issue is trying to use moderate to heavy throttle to accelerate and in the entire 2000-3000 range it can stumble and hesitate - but once I'm past 3000 RPM everything is beautiful.  A third way this manifests itself sometimes is a larger stumble right before 3000 RPM (which is most likely the point at which the VarioCam Plus is making its transition).  All of this stumbling occurs every time I drive the car.  It takes away from the enjoyment of driving as I have to stumble my way from a stoplight or constantly notice the tugging sensation as I try to cruise.  I have a manual transmission.  

I have been to my dealer many times about this.  Since there are no fault codes, they have declared it normal.  I even had a PCNA field tech tell me it was normal.  Am I naive for expecting this new engine to provide smooth acceleration at RPMS below 3000?  On various internet forums it seems many people share my problem, and the threads about this issue are long without resolution.  Sometimes when people flash their ECU or disconnect their battery it seems to be improved for a little while (hours to days) but will eventually return.  It seems to us like it's a software issue in the ECU trying to compensate for some faulty sensor or input somewhere, and in the compensation, it causes fuel/air mixture issues or something else that manifests itself in stumbling.

I would appreciate some suggestions on how to start narrowing down the issue.  Should I replace things like O2 sensors?  Should I flash my ECU with something from a tuner?  Should I find a local independent mechanic with appropriate electrical diagnostic machines?  Anything would help as I start to get serious about solving this issue.  Back in the day before the engine was so controlled by computer, I would start pulling spark plugs and checking for vacuum leaks, but I'm not sure where to start on the newer 991.

Thanks for reading,
Michael Sherman

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