For what its worth, it might be a number of different items causing you problems if by "acting up" you mean misfires and maybe stalling. Before you try replacing the ignition coil, you might consider some less expensive routes.
I would start by seafoaming the engine (if you're not sure what that is, Google it and the general procedures). If you're afraid of damaging your engine, bring the car to a garage and ask them to do it. It wouldn't be that expensive.
After that, you should replace your fuel filter (especially if you put seafoam in your gas tank, which you should).
If you're still having problems, clean out the throttle body. Only then should you consider replacing the ignition coil, as it can be expensive to replace if you can't get one from a salvage yard.