Honda Repair: 93 civic idle fluctuates, coolant system, air bubbles

Question
I have a 93 civic, when I sit at a stop light the engine rev's up and down. it goes from 900rpms to 2200rpms over and over. I replaced the fuel filter, the distributor and cap. none of that helped.

Answer
Mike, when this has happened in the past for me it usually is an indication that the coolant system has air bubbles or a pocket of trapped air in the coolant system. Bleed or add coolant as needed out of the cooling system. Possibly replace the coolant completely. Replace the thermostat as well.