I've never used an air core, but here is a video of someone's air core and Arduino project that might be helpful.
According to Wikipedia, there are four kinds of air core gauges. http://en.wikipedia.org/wiki/Air_core_gauge
There are four common types of rotary actuators :
Physical gauges, in which the needle is attached directly to the value being measured; for example, a mechanical pressure gauge
Analog volt meters or d'Arsonval movements, which consist of a coil and a permanent magnet
Stepper motors, which move in one-notch increments or steps
Air-core motors, as described below
Do you know which one you have? Also, do you have a datasheet or any specs on the gauge?