Steve, this symptom sounds to me like you may have a problem with the temp switch that's mounted on the top of the thermostat housing. There's a hose that runs from the air intake tube to this switch, and from there to the common chamber on the intake manifold. If this switch opens you will get that idle "surging" that you describe. The ECM is monitoring the RPM of the engine. If it sees the RPM going over around say 1600 RPM, AND the Throttle Position Switch is on IDLE, the computer will enter the FUEL CUT MODE (cutting off fuel) until the idle goes back to around 1200 RPM, when it turns the fuel back on again.