Hey Anthony, I have a 95 Eclipse GS 5spd.I need to know some reasons why engine would idle rough(small miss). Car has had complete tune up. battery,plugs,wires,distrib coil,air filter,oil change. When idling ranges(moves up and down) 750-900rpms. Should I change timing belt? or adjust idle torque? What about head gasket? Fuel Filter? There is a little bit of white smoke at times?Check engine light came on but still starts and runs but feels sluggish at accerleration at times(sometimes). Autozone said they couldnt run codes due to my late model. What do you think will improve idling? Also engine coolant always overflows, seems to run hot but not overheat. Faulty thermostat i think? What do you think of all this? Thanks for your time!
Tony

A bouncing RPM reading can indicate a worn Idle Air Control (IAC) motor. It regulates your idle speed and should keep it steady at around 750-800 RPMs. But your idle is not moving too much, so it's probably not that big of an issue right now.

But what is a big issue is if your current timing belt (and balance belt) has over 60,000 miles on it. Get it replaced ASAP if you're near that mileage on those belts. With a timing belt replacement, your tensioner and water pump should also be replaced. A weak water pump may also be the cause for your overheating. But it's a good idea to get a coolant flush, replace your thermostat, and radiator cap along with your timing belt and water pump replacements. You may even want to consider replacing your upper and lower radiator hoses if you're paranoid like me ;-)

If your head gasket was at fault, your car may not even start or would run extremely poorly. But any garage can perform a compression check to verify your head gasket is ok. Though replacing your fuel filter every couple years or 25,000 miles is always a good idea. Remember to replace your transmission fluid every 35k-45k miles as well.
Good luck!