My 3B runs about 18.5-19 inches at idle, fully warmed up, no accessories on. I lose about 2 inches with AC on. Regards, Jerry 91 200qa >>>>>>>>>>>>>>>>>>>>>>>>>>>>> Bill asked: What is a normal vacuum reading at idle. On my autometer boost/vac guage I consistently get 15 inches of vac. What should I be getting? I've heard 17 is normal.