Aerostar surging

Could be caused by one of the following below

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard it and keep testing

Its common for the iac( idle air control) motor to go bad. Check for vacuum leaks first. also look at maf sensor for clean wire in sensor.
Throttle position sensor can cause surge or rolling idle. tap lightly on side of sensor and listen for change in rpm.