My 86 F150 seems (in my opinion) to idle a little high. the on dash tach says high idle is 1500 and reguar idle is 1000. I know that the dash tach is more of a cool toy than a real diagnostic device, but to my ear it also seems a bit fast. I would like to slow it down, or at least get it back to factory specs but do not have manuals. anone have some tips?