Listed as a chengyu, with derivation cited from Lao She's
《骆驼祥子》 (Camel Xiangzi / Rickshaw Boy, 1936):
结结巴巴的,他把昨夜晚的事说了一遍 - 'haltingly, he told over what had happened the night before'. The phrase reduplicates
结巴 'stutter' with the AABB pattern that intensifies adjectives in Chinese.