Generally, a rough idle only when cold is either a vacuum leak (around the fuel injector seal(s)) or faulty fuel delivery--poor injector spray pattern, partially plugged, defective fuel distributor--in increasing cost to fix order.
1) check for vacuum leaks around injector seals by dribbling a water hose on the injectors when you first start the car--if one is leaking, you will hear the 'sucking sound' and a misfire will happen when the water gets sucked in.
2) Run a can of BG-44 fuel injector cleaner to try and clean up the injectors. 3)If you have not been running a 'clean-up' quality gasoline--run abig bottle of TECHRON through system to remove gum deposits from the intake vlaves. It only takes a little crud to soak up the tiny amount of fuel sprayed in at idle and lean out the mixture enough to cause a misfire.
4) Fuel distributor mal-function (damage from rust or debris) would generally show up all the time and a failed diaphraghm in the fuel distributor would cause 'flooded' hot starts and a rich idle.