Get a pressure tester from pelican.
I had a similar problem, for me it was several problems that needed to be sorted. My guess the problem is a broken vacuum line. Here is my troubleshooting if you are interested, it is several pages.
http://forums.pelicanparts.com/porsche-911-technical-forum/664950-1976-911s-garage-find-road-4.html#post6702074
__________________
1976 911S; 1957 Mercedes 190SL; 1982 Ferrari Mondial Coupe; 1991 Nissan Figaro; 2001 Panoz Esperante ; 1969 Pitts S1C
http://forums.pelicanparts.com/porsche-911-technical-forum/664950-1976-911s-garage-find-road.html
|