You probably forgot to clean out your idle air control valve, or forgot to re-connect the wiring harness to it. This little "gizmo" is controlled by the CPU,which gets signals from your O2 sensor to raise or lower idle speed. Do yourself a favor, and install a set of Bosch platinum, Fusion, or nippondenso Iridium or Twin Tip plugs. You will be amazed how much more power is availabe and how much money on gas you save, too!! It is also possible that the ":surge" is a by product of having a dirty O2sensorr. Install a Bosch unit here, too, if things don;'t get better. Also, start using Mobil 0W-30 oil to keep your engine guts clean. You will save money in the long run because you only need to change it every year or year and a half!