I just bought a used '91 Nissan Stanza. everything under the hood is almost brand new, however I'm having a problem with the car, everytime I stop at a light the car starts to shutter. The shuttering doesn't start until the engine gets warm. What is causing this to happen in the car? There have been several things replaced just recently, such as the the fuel injectors, water pump, raditator, and several hoses, and battery. If anyone can help me I would greatly appreciate it. B.