When surging occurs, it usually is due to excessive air going into the intake manifold and following are possible causes.
1. Faulty Intake Air Control (IAC)valve. IAC stuck in open position or not closing due to clogged coolant hoses.
2. Vacumn leakage at intake manifold, could be due to dislodged hoses or faulty PCV.
3. Idling speed adjusted too high.