[93 Cobra needs input]

I still have the factory motor in it with 90,000 miles I was driving the car and it felt like it was running rough around 2,500 at 3,000 it would come out of it almost like a dirt bike power band seems to me it is ignition related, felt like a snomobile with a fouled plug that would come to life then go away. The plugs all look fine but after I cleaned the rotor and distributor cap it stays bad all the time no more coming out of it. At idle it holds 700 rpm fine just a rough feeling and not very snappy throttle response. I'm getting a new cap and rotor and plugs tonight but does anyone think it might be the TFI module. I don't realy know exactly what they do but I know they go bad, Is there any way to check one before giving $105 to ford for a new one?? Sorry for the long post, I just hate electrical problems! The car does have a msd 6al box and blaster 2 coil if that matters.