89 Running Bad

My son's 89 started missing bad today. It idled rough and missed and sputtered when you give it gas, especially a lot of gas. It would miss and sputter until it gained some rpms then run better. I put a set of plugs in and it ran better but still sputtered. Ran it for a while and the idle got worse. Drove it and it sounds and feels like its only running on 3 cylinders at times. It will idle smooth then pop several times out the exhaust then smooth then pop a few times again. I didn't have the tools to check the cap and rotor but that will be next. Any other suggestions on what to check???? It's an 89 GT with about 170000 miles on it.

plug wires and cap

Ok, I ran some seafoam thru it, helped but no dice. Replaced the cap and wires and was worse? I noticed the air intake hose was torn near the manifold. I taped it up and changed out the clamp and it runs better than before the problem started. Thanks for the advice. :clap: :clap: :clap:

you should check all the basics like oil . headers. all the wiring. and the alternater