To see if it's an ignition related problem, try pulling one spark plug wire at a time. Each time you disconnect a plug the engine should run rough but still stay running. Each plug wire should have about the same effect. If you find one that doesn't make a difference, that cylinder is not doing anything. If you cant keep the car running with 1 wire disconnected, theres more than the disconnected plug/cylinder that's not working.
Oh, and you should be able to jump a sparc to ground from each plug wire when you have it disconnected.
How about a wet air filter???