Car chugs when engine is cold..why?

Typically when an engine runs rough on start up then clears, is a sign of a fault in the ignition system. You replaced the distributor but did you also put in new plugs and wires? If so, your coil may be acting up. Take a spray bottle and fill it with water. Mist down your plug wires and coil area. See if the engine bogs down and begins to skip. If all seems well with your ignition system, get some throttle body cleaner and give your throttle body a good clean out. If still no change after cleaning your throttle body, try replacing your ambient air sensor. May be called an Air Charge Sensor on your car.