Hi
How long ago did you give your car a nice tuneup?
I'd change spark plugs, wires, as well as the distributor rotor and cap. Fuel filter change and an oil change are also in order.
Also try to check bettery/alternator behaviour, or have someone who knows what he's doing do that.
And believe me, if you think taht is a pita, you should get to know my car
Still, it could be anything... O2 sensor comes to mind. But I'd start with the obvious, since it's likely that those things need to be changed anyway, right?
Good luck
Alex