whats wrong with my car

[94snake]

i have a 94 cobra and lately it has been running rough. at idle the rpms seem to surge and be rough. sometimes it wants to die if i dont give it gas. when driving their is power loss and the exhaust sounds different. when i get around 4000 rpms it wont rev any higher and sounds like it hits a rev limiter and backfires. i cleaned the spark plugs, air filter and mass air sensor and replaced the fuel filter. could it be timing or what.im clueless