Mazda Premacy engine stops at low velocity or when deccelerating

At first the engine signal light (malfunction indicator) went on. We cleaned the air filter, and changed the sparks. The malfunction indicator light was no longer. The problem following this however, was that when it runs at a constant speed it runs smoothly, but when its decelerating, the engine stops, and that you'll have to start it again. Starting it is okay, but only when decelerating it the engine goes off again.