Before you leave to bring it in, at the very least check the plug wires (the set of six thick wires of all the same color that plug in to the engine in two rows of 3 wires). Make sure that they are plugged in tight. You CAN troubleshoot these by turning the motor on and pulling them out, listening, and plugging them in one at a time.

If you have time to mess around with IMing and Posting here, then you have 5 minutes to check the plug wires.

-MR