car runs rough (just sometimes)

I have a problem with a 95 t bird, 3.8 liter. Car runs rough sometimes, other times you can't even feel it running. No one i've taken the car to knows what the problem is, I start the car one day and it feels like it's missing like crazy, and runs really rough. then the next time i start it, it runs perfect, no missing or shaking. Someone told me to have the trans fluid changed, so i did and theres no difference, also had a complete tune up. Any suggestions? Thanks

Does it only run rough during certain weather conditions (damp)?

Does it only run rough during certain weather conditions (damp)?
no, it actually runs better when its raining, could it be a loose ground somewhere?

Check the computer codes

Check the computer codes
I have had the computer codes checked and nothing comes up, have had the car to 3 mechanics and no one can figure out what the problem is.

im having the same problem and took it to the ford dealership and they did a diagnostic check and couldnt figure it out so if some can help that would be greatly apprectiated

Tonight when it is dark start the engine, pop the hood, and take a squirt bottle of water and squirt down your cap and wires while looking for a pretty blue spark to jump to ground. Next, with the car still running and do this at day or night or whenever, take a can of carb cleaner and spray down your intake where the upper meets the lower and the lower meets the heads. Any change in engine rpm is due to a vacuum leak. Lastly, post on www.tccoa.com and see if the multitude of 3.8 guys there have a clue.

I say plug wires. I know that with changing conditions they can effect the running of you car... though usually it gets worse when raining. I say do the plugs, wires, cap and rotor, that should solve the problem I think, its not very expensive shoudln't cost more than 100 for everything, plus if it doesn't work you won't have to worry about it later... But my vote is going towards your plug wires.

I say plug wires. I know that with changing conditions they can effect the running of you car... though usually it gets worse when raining. I say do the plugs, wires, cap and rotor, that should solve the problem I think, its not very expensive shoudln't cost more than 100 for everything, plus if it doesn't work you won't have to worry about it later... But my vote is going towards your plug wires.
Thanks for all the help, but i,m still having the same problem. I have had the wires, cap,rotor and points replaced, but i still have the same problem. I also have one other problem! When I'm on the highway, the car will just drop out of overdrive, it scuttles back and forth from 4th to 3rd to 4th, it will only stay in third for a second or two, then go right back into overdrive. I've had the car to 2 transmission shops and there are no codes, and no one can figure it out. The car only does these things sometimes, maybe 1 out of 3 times that i take it on the highway.This is driving me nuts because, the car runs perfect other times,and no one can figure out what the problem is. I've had a trans tune up,and complete engine tune up, including changing the wires, cap, rotor,points, and plugs. And cant think of anything else! HELP!!!!