i have a 88 with 5.8...at times it runs rough at idle to the point it will die,but most of the time it runs fine...there no vaccum leaks or bad plug wires,new filters......any help guys
thanks,and lets get`em muddy
donnie

 

Mine did the same thing and it was the throttle body.

 

I would suspect problems with the EGR valve. Hard to prove unless it is stuck open when you are looking at it. You could unhook the vacuum line going to it for a while and see if the problem goes away as long as it is unhooked.