my civic did the same thing and i had to replace the thermostat. after about a year it started acting up again but it was really sporadic like what you are describing so i started looking around under the hood and i found where i hooked a wire into my distributor it had grounded out and "burnt" up right by the engine temp sensor. so that one was my own fault. the temp sensor should be in a similar spot on your engine; just under the distribute on the head itself, its a single wire i believe its yellow with no tracer