I am having a similar problem with my '84 911 Targa. At about 3000 RPM my car exhibits the same symptom of "jerking a bit" until i increase or decrease the RPM.
It's mostly annoying now - but i am concerned it may lead to other problems.
Check out this thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/511423-question-about-cleaning-afm.html
I plan to take a look this weekend at my AFM (Air Flow Meter).
Will subscribe to this thread and hope we both can solve our problem!