My 84 4000 misses bad and will not idlle at all most of the time. This is a bad miss not a slight spit. It is not just one cylinder not hitting it is a serious miss. It makes no difference at what rpm it is run at. It has no power and is unusable. Electrical or fuel?? thanks

 

check all vacuum pipes/clean the idle control/bypass valve and pipe work check the main vacuum pipe under the inlet manifold ( the pipe comes of the top of the rocker cover and goes under the inlet manifold and is a common cause for breaking down and rubber rotting

 

Had a 4000S with similar problem, tensioner pulley froze and belt skipped two teeth.