Check and recheck the ground connections and wires, if there's any play or any damage along those wires, the starter will act all razy like that and only fire up when it has the perfect connectionOk...now this old mechanic is scratching his head. I replaced the starter and it works great...sep for the fact Im still having the same problem. What gives? It starts up perfectly fine...when it wants to. Every once in a while, the starter will not engage...the solinoid kicks but the starter wont kick on.