need opions on motor

recently my 318 has been running rough i changed plugs tonite and now it idles up and down if i go to put it in drive it shuts off if im not pedaling the throttle any ideas anyone i also adjusted the carb usig vaccum gauge for idle somewhere in the mix something is wrong i had to adjust idle screw up just to get here to work tonite so if you can let me know what to try next thanks