Idle speed has sped up
 

Hi, I have a 1971 911E , anyone know where/how I set the idle speed at? It had been set to about 2000 rpm but for some reason has started jumping to 4000 rpm. It feels sort of like the throttle is sticking, i can actually pull the gas pedal back and the idle drops. After I press the pedal and release it, the idle finds its way back to about 4000. The choke still seems to work the way it's supposed to, so it's not like the manual choke is ON all the time. Any ideas? places to start looking? thanks!