2001 Other Mazda Models #3 cylinder misfire

When I Start my car up on a cold start it sounds as if it wants to die out and runs very badly we have changed the coils we have put a idle control on it we have put a fuel pump on it too we just can't figure out what the problem is and I have been talking it back to the dealership. I have have spark plugs done and had the fuel injections cleaned too. I Have A Mazda Tribute