It may not be a spark issue? Check for trouble codes. Some of the national brand autostores used to check some codes for free. If you have a digital multimeter you can do an inductive test on the plug wires, engine running, You don't take the plug wire loose and don't penetrate the insulation. You ground one lead of meter to chassis, the other lead just touch the plug wire, it should give some kind of reading. You compare the readings from one cylinder to the next. Say, most cylinders show around 1/2 volt then one or or two show close to zero. Check the coil for the ones that show zero. The test isn't conclusive, but, it is fast, if there is a spark issue. With engine running, be careful around belt and pulleys.