High Idle Problem on 75 911
 

Just replaced the airbox on a 75 911 along with new intake gaskets, intake boots and all orings for cold start valve, throttle body and coffin gasket for air flow meter. Car now has an idle of around 1500 rpms even with the air bypass screw all the way in. The idle will fall very slowly down to around 1000 rpms after reving the engine taking about 10-15 seconds to do so. Any ideas on where to start to look?. I did install a popoff valve as well. Thanks in advance. Bill

Throttle linkage.
Springs on linkage.

I was just tightening my linkage over the weekend and had a similar problem until I rotated one ball cup 360'.
Just a guess.

I assume that the car did not do this before you changed the air box? You must already know the answer - you have an air leak. Classic symptoms - you are getting air in from somewhere, and your idle screw is no longer the only path for extra air to get in there. Time to retrace your steps.