My '77 911s just started with a new mystery. At idle ( 1100-1200) it was fine until I drove for a while. Then when ever I stopped the idle would slowly climb up to 22-2300. Stopped at a local P-car wrench and showed him the problem. He said something about there being a leak into the air box or something. Nursed it home and all of a sudden the problem went away and stayed away for the rest of the day on trial runs. HELP with any ideas
