I have a 98 cherokee i just bought off an army buddy,he told me it had no heat,and it had a "random cough" he had just put a new radiator in it trying to fix heat prob..as it turned out i took the head off to replace head gasket,it was cracked in three places.replaced with low mileage 2000 4.0 head.the random cough he mentioned is my problem..i cant cure it!! it starts fine runs great,then randomly coughs through the throttle body. I hear the IAC openeing up making that loud sucking air noise when its acting up.but if i shut it off an restart it goes away and runs fine..it also randomly idles from high to low(sounds like im at a stop light reving the engine at a ferrari like i wanna race) again shut it off an restart its fine.
ok i have replaced every sensor except crank pos,including pick up in distributor..newer head off 2000,new fuel pump w/filter and regulator.throttle pos(which i was sure was the prob) IAC,air temp,map,injectors,coil,plugs,wires....i have noticed that at night i can see faint arking around the spark plugs..very faint..Im at a loss here any ideas?

 

You should not see any sparking around any part of the ignition system, there is part of your problem. Look for vacuum leaks around the intake manifold gasket before throwing any more parts at this thing.