94 chevy camaro problem

i have a 94 chevy camaro. The problem is that my car doesnt go fast any more and runs kind of rough. My friend says that it could be the air filter becasue i've lost horse power but i dont know so can you give me some suggestions on what i can do instead of taking it to the dealer

- edit - the engine is V6 3.4 it runs rough all the time. when the service light goes on then the car makes exhaust sounds different, i cleaned my air filter about 2 or 3 weeks ago in water and dish soap. Sorry about not enough info

does it run rough all the time? certain rpm's? more details please

It could be any number of things, clogged air filter (easy to check and fix), slightly clogged exhaust system, engine troubles (Head gasket, etc.) keep an eye on your fluids if your coolant is constantly low it could be a head gasket. Also, it helps us help you if you give us more specifics like what engine is in the car...V6 3.4L, V8 LT1... etc.

Tap your cat, does it rattle? IS there a rotten egg smell?

It could also be a clogged fuel filter/fuel line or maybe you got a bad tank of gas... As others said, we need more details

if the exhaust sounds different and it runs rough at certain rpm's i would almost put money on the cat being clogged..

well how about a simple tune up....that should be the first thing you ask yourself, when was the last time u had one? that would have been my first thought, loosing power car feeling rough, hell maybe she needs some plugs wires oil and all that other good stuff.