Reducing EMI in AVR

What will be the solution for reducing the EMI generated by spark coil. As I am using an on board relay as a switch for that spark coil. And that sparker is totally isolated in terms of power supply. It works on seperate 1.5V battery.
But still I think because of relay coil the noise is coming in my circuit. Suggest any simple method if known. Cause my controller is malfunctioning on few occasions.
Thanks in advance.

A spark is a wide bandwidth transmitter - the early morse code transmitters just used a spark to transmit the signal. Sheilding is probably your best bet to reduce EMI. Aluminum foil is a great cheap way to create sheilding - just make sure you don't short anything out.