Simple things first. Check the condition of the plugs, wires, cap and rotor. How bout the fuel filter, has that been done recently? Follow all of the rubber vacuum lines from the throttle body and check for leaks or broken lines.
Here's a quick test you can do before doing anything. While it is idling, spray down the ignition wires and distributor cap with water. Not a high pressure spray, just a good mist. See if anything changes. This works well in the dark and you will actually see if spark is jumping from the wires.