Little sputter, little lurch with auto heat

[mkimber]

As I driving my 87 Carrera home from its 4-1/2 month winter hibernation, I decided to check heating, ventilation and a/c controls. Cruising about 85 mph on the expressway (with the engine full warmed up), I quickly turned automatic temp. control knob to from 0 to #7. The engine sputtered a bit (a boxer burp, maybe?) and the car lurched a little. I repeated the same thing three more times, with the same result.

Has anyone else experienced this before or know what's going on? I have the prayer candles lit in hopes that it is nothing serious.