if i set my idle at 800 it will do the same thing. some place i read where you should have your idle set at 1000 for 4spd 6pk cars. i run mine at 950 and its fine. i will try to find that info. hope this helps. i know it dosen't answer your question as to why this happens. someone should know otherwise why would it be to have the idle set at 1000rpm. maybe mike at dayclona would know?